'apus' originates from Modern Latin, specifically the word 'Apus', ultimately from Greek 'Apous', where the prefix 'a-' meant 'without' and 'pous' meant 'foot'.

'apus' changed from Modern/Medieval Latin 'Apus', borrowed from Greek 'Apous', and was later adopted into English as the name of a constellation and a genus.

Initially it meant 'without feet', referring to the bird-of-paradise thought to lack visible feet; over time it became a proper name for a constellation and for a genus of birds.