'apneumatic' originates from Greek elements: the privative prefix 'a-' meaning 'not' and 'pneumatikos' (from 'pneuma') meaning 'of or relating to breath/air', ultimately from Greek 'pneuma' meaning 'breath, wind'.

'pneumatic' entered English via Latin/French from Greek 'pneumatikos'; 'apneumatic' was formed in modern scientific English by adding the prefix 'a-' to 'pneumatic' to denote absence of air-filled spaces, appearing in technical contexts from the 19th century onward.

Initially related to 'breath' or 'air' (as in 'pneumatic'), the compounded form came to mean 'without air' in a structural/anatomical sense — i.e., lacking air cavities — and retains that specialized meaning in modern usage.