'Apus' originates from Modern Latin/New Latin, ultimately from Greek 'apous' (ἀπούς), where the prefix 'a-' meant 'without' and 'pous' (ποῦς) meant 'foot'.

'Apus' was adopted into New/Modern Latin from the Greek word 'apous' meaning 'without foot'. The name was used for the bird-of-paradise in early modern European writings and later applied to the southern constellation and to the bird genus 'Apus'.

Initially, it meant 'without feet' (a belief about bird-of-paradise specimens). Over time the term came to be a proper name applied to a constellation depicting the bird and to a genus of swifts (birds notable for very short legs), losing the literal sense for most modern uses.