- A ... A-4
- A-6 Intruder ... AAFC
- Aag ... Abadgaran-e Iran-e Islami
- Abadi, Haider al- ... Abbe limit
- Abbe sine condition ... ʿAbd al-Raḥmān I
- ʿAbd al-Raḥmān ibn Dhū an-Nūn ... abduction
- abduction ... Abelian theorem
- Abell, A.S. ... abhimukhī
- Abhinavagupta ... Abney, Sir William de Wiveleslie
- abnormal gas exchange ... Abraham, Plains of
- Abraham, Spencer ... Absence, The
- Absent-Minded Professor, The ... Abtsbessingen faience
- Abu ... Abū Ḥudhayfah
- Abū Hureyra ... Abū ʿAbd Allāh Muḥammad ibn Idrīs ash-Shāfiʿī
- Abū ʿAbd Allāh Muḥammad ibn Ismāʿīl al-Bukhārī ... abyssal cone
- abyssal gap ... açaí
- acai ... accelerating potential
- accelerating voltage ... Account of Corsica, The Journal of a Tour to That Island; and Memoirs of Pascal Paoli, An
- Account of My Hut, An ... Acer rubrum
- Acer saccharinum ... Achelous River
- Achelousaurus ... acid leaching
- acid lead ... Acomys subspinosus
- Aconcagua River ... Acre
- Acre ... Act in alteration of the several acts imposing duties on imports, An
- Act in Restraint of Appeals to Rome ... action integral
- Action Jackson ... actual sin
- Actual Size ... ad verecundiam
- ad watch ... Adam, Karl
- Adam, Lambert-Sigisbert ... Adamson, Andrew
- Adamson, Joy ... Addington, Henry, 1st Viscount Sidmouth of Sidmouth
- Addington, Maybelle ... Adelphi
- Adelphi ... adhyatmavidya
- adhyatmika ... adjuvant chemotherapy
- Adkins v. Children’s Hospital ... Admonitions of the Court Instructress, The
- admonitory mask ... Adranum
- Adrar ... adult-onset diabetes
- Adultério ... Adventures of Mark Twain, The
- Adventures of Master F. J. ... Aedes aegypti
- Aedes albopictus ... Aenaria
- Aeneas ... Aeronomy of Ice in the Mesosphere
- aerophone ... Aethionema cordifolium
- Aethionema grandiflorum ... Affleck-Boldt, Caleb Casey McGuire
- Affliction ... Africa Rekk
- Africa Speaks ... African National Congress Women’s League
- African National Congress Youth League ... Afrique Équatoriale Française
- Afrique Occidentale Française ... aftershock
- Aftershocks ... Agapornis roseicollis
- Agar ... Age of Heroes, The
- Age of Innocence, The ... aggregate
- aggregate ... Agnelli, Umberto
- Agnes ... Agrarian Problem in the Sixteenth Century, The
- agrarian reform ... Agro Marshes
- Agro Pontino ... Agyriales
- Agyrtidae ... Aḥmad ibn Ḥanbal
- Aḥmad ibn Ibrāhīm al-Ghāzī ... Aḥsāʾī, al-
- Ahson at-taqasim fi marifat al-aqalim ... Aiken, Howard Hathaway
- Aiken, Joan ... Air America Radio
- Air and Simple Gifts ... Air, Waters, and Places
- air-blast tunnel freezer ... Airy hypothesis
- Airy model ... ʿAjjul, Tall al-
- Ajka ... Akbia
- AKC ... Akinola, Peter
- Akinola, Peter Jasper ... Akula
- akund floss ... Alabama Polytechnic Institute
- Alabama River ... Aland, Kurt
- Alang language ... ʿAlawīyah
- Alax You Qi ... albatross
- Albatross Plateau ... Albert, Edward
- Albert, Eugen d’ ... Ålborg akvavit
- Albornoz, Gil Álvarez Carrillo de ... Alcatraz, Battle of
- Alcayaga, Lucila Godoy ... alcoholic hepatitis
- Alcoholics Anonymous ... Aldrovandi, Ulisse
- ale ... Aleph and Other Stories, 1933–1969, The
- aleph-null ... Alexander III
- Alexander Island ... Alexandria University
- Alexandria, Library of ... Alfonso el Magnánimo
- Alfonso el Magno ... Algebraic Versus Transcendental Objects
- Algeciras ... ʿAlī ibn Abū Ṭālib
- ʿAlī ibn Būyeh ... alienation effect
- Aliénor d’Aquitaine ... alkaline extraction
- alkaline fuel cell ... All Jammu and Kashmir Muslim Conference
- All Men Are Brothers ... All-hallown summer
- All-India Committee ... Allegory of the Missionary Work of the Jesuits
- Allegory of the Reign of Rudolf II ... Allende Gossens, Salvador
- Allende meteorite ... alligator fish
- alligator gar ... Allston, Robert
- Allston, Robert Francis Withers ... Almond, Gabriel
- Almond, Gabriel Abraham ... Alor Setar
- Alor Star ... Alpha Tauri
- Alpha Ursae Minoris ... alpine vegetation
- Alpine-Himalayan System ... altazimuth system
- Altcoins, coins, and tokens: What’s the difference? ... Altman, Klaus
- Altman, Robert ... aluminum-manganese-silicon alloy
- aluminum-spinel series ... Am
- AM ... Amanda Knox
- Amanda Smith Industrial School for Girls ... Amaterasu Ōmikami
- Amateur ... amazonite
- Amazonomachy ... Ambondro mahabo
- Ambonese ... Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field, Convention for the
- Amelioration of the Condition of the Wounded, Sick, and Shipwrecked Members of Armed Forces at Sea, Convention for the ... American Academy of Arts and Sciences
- American Academy of Pediatrics ... American Cereal Company
- American Challenge, The ... American Folk Art Museum
- American Folk Art, Museum of ... American IV: The Man Comes Around
- American ivy ... American persimmon
- American Petroleum Institute gravity scale ... American Smooth
- American Sniper ... American yew
- American yew ... Amherst, Sir Jeffery
- Amherst, William Pitt ... AMISOM
- Amistad ... Amne Machin
- Amnesia ... amorphous substance
- amortization ... amphisbaenian
- Amphisbaenidae ... Amstelveen
- Amsterdam ... amylase
- amylo-1:4,1:6-transglucosidase ... Anaconda Company
- Anaconda Copper Mining Company ... analogue modulation
- analogue signal modulation ... Ananke
- Ananse ... Anastasius IV
- Anastasius Sinaita, Saint ... Ancestress, The
- ancestrula ... Ancylostoma duodenale
- ancylostomiasis ... Anderson
- Anderson ... Andersson, Wilhelm Carl Emil
- Andersson. Eva Magdalena ... Andreessen, Marc
- Andreev, Leonid Nikolayevich ... android
- Android ... anemochory
- anemometer ... Angela’s Ashes
- Angelarius ... Angiostrongylus
- Angiostrongylus cantonensis ... Anglo-French Treaty
- Anglo-French Treaty ... Angst des Tormanns beim Elfmeter, Die
- Angst essen Seele auf ... aniline ink
- aniline printing ... Anio River
- anion ... Anna Comnena
- Anna Karenina ... Anne, Act of
- Anne, Lady ... annulene
- annulment ... Anoplius fuscus
- Anoplophora glabripennis ... Anselm of Baggio
- Anselm of Canterbury, St. ... antagonistic behaviour
- antagonistic coevolution ... anterior nasal diphtheria
- anterior nuclear group ... Anthony, Susan B.
- Anthony, Susan Brownell ... Anti-Pamela
- anti-poetry ... Antidote
- antidote ... Antimorona
- antimuon ... Antiquitates rerum humanarum et divinarum
- Antiquités de Rome ... Antonelli, Giacomo
- Antonello da Messina ... anubhava
- Anubis ... Anzoátegui
- Anzúrez, Pedro de ... Apalachicola River
- Apalategui, José Xavier Zubiri ... APG IV
- Apgar score ... Apis florea
- Apis koschevnikovi ... Apollinaris Sidonius
- Apollinaris The Younger ... Apopi
- Apopis ... Appaloosa
- Appaloosa ... Apple Cart, The
- Apple Computer, Inc. ... approach-approach conflict
- approach-avoidance conflict ... Apurímac River
- Apurímac, Río ... Aquila
- Aquila audax ... Araba
- ʿArābā al-Madfūnah, Al- ... Arad
- ʿArad ... Aranjuez
- Aranjuez Gardens, Marquis of the ... Arber, Werner
- Arbëresh ... ArcelorMittal
- ArcelorMittal Orbit ... Archer
- Archer ... Archiv für Entwicklungsmechanik der Organismen
- Archiv für pathologische Anatomie und Physiologie, und für klinische Medizin ... Ard Mhacha
- Ard Mhacha ... Are Sand Dollars Alive?
- Are Song Lyrics Poetry? ... Areopagite Council
- Areopagitica ... Argentine Confederation
- Argentine Dogo ... Argyll, Archibald Campbell, 10th Earl and 1st Duke of, Marquess Of Kintyre And Lorne, Earl Of Campbell And Cowall, Viscount Of Lochow And Glenyla, Lord Of Inverary, Mull, Morvern, And Tirie
- Argyll, Archibald Campbell, 1st marquess and 8th earl of ... Arihant
- Ariidae ... Aristoxenus
- Arita ... arkose
- arkosic arenite ... armed bullhead
- armed force ... Armorica
- Armorican Massif ... Arnault, Bernard
- Arnaut Daniel ... Arnulf of Metz, Saint
- Arnulf the Elder ... arrak
- Arran ... Arrow War
- Arrow’s theorem ... Art
- ART ... Art Ross Memorial Trophy
- Art Ross Trophy ... Artemisa
- Artemisia ... Arthur, Jean
- Arthur, Joseph Charles ... artist
- Artist Formerly Known as Prince, the ... Arum palaestinum
- Arum vokzal ... as
- As a Man Grows Older ... Asarum europaeum
- Asase Yaa ... ascolichen
- ascoma ... Ashburnham, John
- Ashburton ... Ashmarthya
- Ashmat Shomron ... Asian American and Pacific Islander Heritage Month
- Asian badger ... Ask the Posts of the House
- Askalon ... Aspects of the Theory of Syntax
- Aspegren, Chuck ... Assamese literature
- Assange, Julian ... assimilation efficiency
- assimilation model ... Assumption of the Virgin
- Assumption of the Virgin ... astillero, El
- Astin, Patty Duke ... Astronauci
- astronaut ... Asyūṭ Barrage
- Asyūṭ Dam ... Atarashii hito yo meza meyo
- ataraxia ... Athalie
- Athamas ... Athis-sur-Orge, Treaty of
- Athlab, Mount ... Atlantic & Pacific Tea Company
- Atlantic and St. Lawrence Railroad ... Atlas Tellien
- Atlas, Charles ... atomic fluorescence spectrometry
- atomic fluorescence spectroscopy ... Atrichornis clamosus
- Atrichornis rufescens ... Attenborough’s pintail
- Attenborough’s pitcher plant ... ATV
- ATV ... Auction of Lives, The
- Aucuba japonica ... auger
- auger boring ... Augustinian Recollect
- Augustinians of the Assumption ... Auramazda
- Aurandt, Paul Harvey ... Auschwitz-Birkenau State Museum
- Auschwitz-Birkenau. The Nazi German Concentration and Extermination Camp (1940–-1945) ... Australia, colonization of
- Australia, Commonwealth of ... Australian pitcher plant
- Australian Plate ... autarchy
- autarkei ... autogiro
- autograft ... autonomic nervous system
- autonomous car ... av bet din
- Ava ... Avenant, Sir William D’
- Avenarius, Richard ... Aveyron, wild boy of
- Avezzano ... Avon Products, Inc.
- Avon, River ... Awo
- Awokanak ... Axis Age
- Axis axis ... Áyios Nikolaos
- Áyios Stéfanos ... Azad, Chandra Shekhar
- Azad, Chandrashekhar ... ʿAzīz-ud-Dīn ʿĀlamgīr II
- Azizam ... aʿyān
