- A ... A-Team, The
- A-type star ... Aargau
- Aargau ... Abate, Niccolò dell’
- Abate, Nicolò dell’ ... Abbott, Robert
- Abbott, Robert ... ʿAbd Allāh ibn Saʿd ibn Abī Sarḥ
- ʿAbd Allāh ibn Saʿūd ... Abdullah, Abdullah Ahmed
- Abdullah, Farooq ... Aberdeen, George Hamilton-Gordon, 4th earl of, Viscount Gordon of Aberdeen, Viscount of Formartine, Lord Haddo, Methlick, Tarves, and Kellie
- Aberdeen, University of ... AbioCor artificial heart
- Abiodun ... abortifacient
- abortion ... Abreha
- Abreu Freire Egas Moniz, António Caetano de ... Absolutist, The
- absorber layer ... Abū al-ʿAbbās
- Abū al-ʿAbbās Aḥmad ibn Aḥmad al-Takrūrī al-Massūfī ... Abu Sahl
- Abū Sahl al-Kūhī ... Abuná, Río
- abundance ... Académie Française
- Académie Parisienne ... Acarida
- Acarie, Barbe-Jeanne Avrillot, Mme ... Acción Democrática
- Acción Democrática Nacionalista ... acedia
- Aceh ... Achaemenian dynasty
- Achaemenid dynasty ... Achras
- Achras zapota ... Acme Colored Giants
- Acmeists ... acquiescence
- acquired character ... Acruvium
- Acrux ... actinon
- Actinophrys sol ... Acton Technical College
- Acton, Brian ... Ad Astra
- Ad Atticum ... Adam the Hunchback
- Adam Thoroughgood House ... Adams, Walter
- Adams, Walter Sydney ... Adderley Street
- Adderley, Cannonball ... Adelheid die Heilige
- Adélie Coast ... Adhikāranandin
- adhipati-pratyaya ... Adjutantenritte und andere Gedichte
- adjuvant ... Admonitions of the Court Instructress, The
- admonitory mask ... Adrar
- Adrar ... adultery
- Adultery and Other Choices ... Adventures of Roderick Random, The
- Adventures of Sherlock Holmes, The ... Aedesius
- aedicula ... Aeolian Islands
- Aeolian mode ... aerospace engineering
- Aerospace Industries Association of America ... Aetolia
- Aetolian League ... affricate
- Afghan ... African art
- African arts ... African popular music
- African Portraits ... Afro-Shirazi Party
- Afroasiatic languages ... Aga Khan
- Aga Khan I ... Agassi, Shai
- Agassiz Peak ... Ageladas
- Agelaius phoeniceus ... Aghstev
- Agi-ga-u-e ... Agnone Tablet
- agnosia ... Agricultural Adjustment Act
- Agricultural Adjustment Administration ... Agua Caliente
- Agua Fria National Monument ... Ahaz
- Ahaziah ... Ahmadu Hammadi Bubu
- Ahmadu ibn Hammadi ... AIADMK
- Aiakeia ... AIM-9 Sidewinder
- aim-point error ... Air Jordans
- Air Lanka ... airbrush
- airbrush art ... Aix-la-Chapelle, Treaty of
- Aix-les-Bains ... akadinda
- Akagera National Park ... Akhḍar, al-Jabal al-
- Akheloios ... Akron
- Akron Art Museum ... Al-Idrīsī
- al-Idrīsiyūn ... Alamanni
- Alamanni, Luigi ... Alaska, University of
- Alaskan brown bear ... Albanian literature
- Albanian Orthodox Church ... Albert Lea
- Albert Memorial ... Albinoni, Tomaso Giovanni
- Albinovanus Pedo ... alcaic
- Alcalá de Guadaira ... Alcmaeon
- Alcmaeon ... Aldington, Edward Godfree
- Aldington, Richard ... Alekseyevna, Yekaterina
- Alekseyevsk ... Alexander Aetolus
- Alexander Archipelago ... Alexandra Falls
- Alexandra Palace ... Alfie
- Alfie ... algebra, elementary
- algebra, fundamental theorem of ... ʿAlī
- Ali ... Alice’s Restaurant
- Alicia Alonso Ballet Company ... alkalemia
- alkali ... All Hands on the Bad One
- All I Desire ... All-China Anti-Japanese Federation of Writers and Artists
- All-China Anti-Japanese Writers Federation ... Allegory of Divine Providence and Barberini Power
- Allegory of Divine Wisdom ... Allen, William
- Allen, William Hervey, Jr. ... alligator apple
- Alligator Baby ... allspice jasmine
- Allstate Corporation ... Almond, Edward M.
- Almond, Edward Mallory ... Alorna, Marquesa de
- Alós, Concha ... alpha wave
- alpha-1 antitrypsin ... Alps
- Alps ... alte und der neue Glaube, Der
- Altena ... alto oboe
- Alto Paraguay craton ... Alva, Fernando Álvarez de Toledo y Pimentel, 3er duque de
- Alva, Tony ... Amadeus
- Amadeus ... Amanita verna
- Amanita virosa ... Amatique Bay
- Amatique, Bahía de ... Ambassidae
- Ambato ... Ambrose Light
- Ambrose of Camaldoli ... Amenhotep I
- Amenhotep II ... American Automobile Association
- American avocet ... American copper butterfly
- American Cordilleran mountain system ... American harvest mouse
- American hazelnut ... American Made
- American Madness ... American Quartet
- American Quaternary Association ... American system
- American Tabloid ... Amerindian
- Ameriprise Financial, Inc. ... amikacin
- ʿamil ... Ammiṣaduqa
- ammocoete ... Amon
- Amon Carter Museum of Western Art ... amphibian
- amphibian chytrid ... ampullar pregnancy
- Ampullaria ... Amur leopard
- Amur maple ... AN/FPS-16
- AN/TPS-71 ... Anaia, Pedro de
- Anaia, Pêro de ... Anami Batsu
- anamnesis ... Anas penelope
- Anas platalea ... Anatomy of Melancholy, The
- Anatomy of Peace ... Ancient Society, or Researches in the Lines of Human Progress from Savagery through Barbarism to Civilization
- ancient Spanish chant ... Andean civilization
- Andean Community ... Anderson, Sherwood
- Anderson, Signe ... André, John
- André, Maurice ... Andrias
- Andrias davidianus ... Andy Hardy Gets Spring Fever
- Andy Warhol Foundation for the Visual Arts ... Angel Island Immigration Station
- Angel Landing ... angiogenesis
- angiogenesis inhibitor ... Anglo-America
- Anglo-American ... Angra dos Reis
- Angra I ... Anicetus, St.
- Anicius Olybrius ... Animals, the
- animation ... Anna
- Anna ... Anne of Austria
- Anne of Brittany ... annular strip
- annulated sea snake ... anophthalmia
- Anoplius depressipes ... Anselm of Canterbury, St.
- Anselm of Laon ... Antal
- Antalcidas, Peace of ... anterior superior alveolar nerve
- anterior uveitis ... anthoxanthin
- Anthoxanthum ... Anti-Slavery Society
- Anti-Slavery Society ... antiepileptic drug
- antiestrogen ... antineutron
- anting ... Antiquities of Warwickshire
- antirabies serum ... Antoninus Augustus
- Antoninus Pius ... Anuradhapura
- anuran ... Aoibhinn, An Craoibhín
- aoidoi ... apapane
- Apapocuva ... Aphelocoma coerulescens
- Aphelocoma insularis ... Aplodinotus grunniens
- Aplodontia rufa ... apollo butterfly
- Apollo Epicurius, Temple of ... Apostle of California
- Apostle of the Alleghenies ... Appeal to the Christian Women of the South, An
- Appeal, Court of ... Apple, Max Isaac
- Apple, The ... apriorism
- Aprista movement ... AQP2
- ʿAqqād, ʿAbbās Maḥmūd al- ... Aquitaine
- Aquitaine Basin ... Arabian Gulf
- Arabian horse ... aragonite
- aragonite group ... Aratus
- Aratus ... arbovirus
- Arbroath ... archaeological chronology
- archaeological museum ... Archie
- Archie Bunker’s Place ... Arctic
- Arctic air mass ... Ardennes
- Ardennes, Battle of the ... Arenaria interpres
- Arenaria melanocephala ... argent
- Argenta ... Arguin Island
- Arguloida ... Aricept
- Arichis II ... Aristobulus of Paneas
- aristocracy ... Arkansas River
- Arkansas River Navigation System ... Armant
- armas secretas, Las ... Armitage, Karole
- Armitage, Simon ... Army War College
- army worm ... Arnoul le Grand
- Arnoul le Vieux ... Arquette, Rosanna
- Arquipélago da Madeira ... Arrokoth
- Arromanches ... arslan
- Arslan ibn Toghrïl ... art patronage
- Art poétique ... Artemidorus
- Artemio Franchi ... Arthur’s Theme (Best That You Can Do)
- Arthur, Bea ... Artist of the Floating World, An
- artist’s fungus ... Arun
- Arunachal Pradesh ... As I Am
- As I Crossed a Bridge of Dreams ... asbab-e sittah-zarooriah
- Asbaje, Juana Ramírez de ... Ascophyllum
- ascorbate ... Ashby, William Hal
- Ashby-de-la-Zouch ... ashoog
- Ashot Bagratuni the Carnivorous ... Asian giant hornet
- Asian ginseng ... Asmar, Tall al-
- Asmara ... Aspergillus nidulans
- Aspergillus niger ... assault amphibian vehicle
- assault and battery ... associated gas
- Associated Merchandising Corp. ... Astarte
- Astarte ... Astoria
- Astoria ... Asturias-Leyenda
- Asturica Augusta ... AT&T Corporation
- AT&T Park ... ATCS
- Atdabanian Stage ... Athenais
- Athenäum ... Atkan Aleut language
- Atkins v. Virginia ... Atlantic slipper shell
- Atlantic South Equatorial Current ... Atocha Station
- atol ... Atopogale cubana
- atopy ... attack, angle of
- Attacus atlas ... Atto Adalbert
- attornatus ... Auburn University
- Aubusson ... Auerbach, Berthold
- Auerbach, Erich ... Augusta Victoria
- Augusta Vindelicorum ... Aung San Suu Kyi
- Aungerville, Richard ... auroral electrojet
- auroral oval ... Australasia
- Australasian Football Council ... Australian lungfish
- Australian Merino ... Austro-Prussian War
- Austro-Russian agreements ... autocephalous church
- Autocephalous Orthodox Church of Poland ... Automobile Club de France
- Automobile Club of Switzerland ... auxiliary sailboat
- auxiliary storage ... Avebury Circle
- Avedon, Richard ... Aves, Isla
- Aves, Islas de ... avoidance relationship
- avoidance, principle of ... Awkward Age, The
- awl ... Axiothella
- axis ... Ayion Óros, Gulf of
- Áyios Dimítrios ... Azad, Chandra Shekhar
- Azad, Chandrasekhar ... azlon
- ʿAẓm Palace ... aʿyān
