1. Impossible to deny or disprove
   "an irrefutable argument"
   - incontrovertible, positive

See also: undeniable

• genus Alyssum
• genus Alytes
• genus Amanita
• genus Amaranthus
• genus Amaryllis
• genus Amauropelta
• genus Amazona
• genus Amberboa
• genus Ambloplites
• genus Amblyrhynchus
• genus Ambrosia
• genus Ambystoma
• genus Ameiurus
• genus Amelanchier
• genus Amia
• genus Amianthum
• genus Ammobium
• genus Ammodytes
• genus Ammotragus
• genus Amoeba
• genus Amorpha
• genus Amorphophallus
• genus Amphibolips
• genus Amphicarpa
• genus Amphicarpaea