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- Aaron
- Aaron's Beard
- Aaron's Flowering Rod
- Aaron, Charles Dettie
- Charles Dettie Aaron
- Hank Aaron
- 'Hammerin' 'Hank' Aaron
- Aarvak
- Aarskog, Dagfinn
- Dagfinn Aarskog
- Abaddon
- Abadie, Jean Marie Charles
- Jean Marie Charles Abadie
- Joseph Abadie's Sign
- Abaris
- Abba
- ABBA
- Abakovsky, Valerian
- Valerian Abakovsky
- Abakovsky Aerowagon
- Abbasids Coin
- Coin of the Abbasids
- Abbey Lubber
- Abbotts Bromley Horn Dance
- Abbott, William Louis
- William Louis Abbott
- Abbott's Booby
- Abbotts Crested Lizard
- Abbott's Skimmer
- Abbott's Day Gecko
- Abbott's Duiker
- Abbott's Moray Eel
- Abbotts Robber Frog
- Abbotts Starling
- Abbott's Sunbird
- Alsophila Abbottii
- Abbott Tube
- Abbott, William Osler
- William Osler Abbott
- Abbott, Wallace Calvin
- Wallace Calvin Abbott
- Abbott's Babbler
- Abbott of Misrule
- A B C
- ABC Trial
- Abdera
- Abderus
- Abdiel
- Abdullah
- Abdallat, Adnan
- Adnan Abdallat
- Abderhalen, Emile
- Emile Abderhalen
- Abderhalden Drying Pistol
- Abdims Stork
- Abe, Shinzo
- Shinzo Abe
- Abel, Niels
- Niels Abel
- Abelia Chinensis
- Abel, Clarke
- Clarke Abel
- Rudolf Abel's Bacillus
- Abel
- Abelard and Heloise
- Abelin, Isaak
- Isaak Abelin
- Abelson, Philip Hauge
- Philip Hauge Abelson
- Aberdeen
- Aberdeen Color
- Abercrombie, John
- John Abercrombie
- Abercrombie's Disease
- Abercrombie, David Thomas
- David Thomas Abercrombie
- Fitch, Ezra Hasbrouck
- Ezra Hasbrouck Fitch
- Abernethy Biscuits
- Abernethy, John
- John Abernethy
- Abhyankar, Shreeram Shankar
- Shreeram Shankar Abhyankar
- Abert's Towhee
- Abert, James William
- James William Abert
- Abrams, Albert
- Albert Abrams
- Abigail
- Abney, William de Wiveleslie
- William de Wiveleslie Abney
- Abney Effect
- Abney Level
- Abrikosov Lattice
- Abrikosov, Alexei
- Alexei Abrikosov
- Abraham
- Abrahamic Covenant
- Abraham's Gate
- Bosom of Abraham
- Abraham Man
- An 'Abraham Newland'
- Abraxas
- Abstract Numbers
- Abswurmbachite
- Absinthium, Artemisia
- Artemisia Absinthium
- Absinthe
- Absinthe Color
- Accidental Color
- Ace
- Acanthus
- Acantha
- Achaemenes
- Aceldama
- Achemon
- Achemon Sphinx
- Achenbach, Walter
- Walter Achenbach
- Acheron River
- Achard, Emile
- Emile Achard
- Achilles
- Achillea
- Achille's Paradox
- Achilles Heel
- Acheulean
- Achelous
- Acid Test
- Acid House
- 'A is for Acid'
- Acol
- ACME
- Ackerman, Lauren
- Lauren Ackerman
- Acosta's Syndrome
- Jose Acosta's Syndrome
- Acrostic
- Acton, John Dalberg
- John Dalberg Acton
- Actaeon
- Actresses
- Ada Lovelace Award
- Ada Programming Language
- Ada Byron of Lovelace
- Ada Aurantiaca
- Adamite
- Adamkiewicz, Albert Wojciech
- Albert Wojciech Adamkiewicz
