'double-concave' is a compound formed from 'double' and 'concave'. 'double' originates from Old French 'double' (from Latin 'duplus'), where 'duplus' meant 'twofold'; 'concave' originates from Latin 'concavus', where the prefix 'con-' meant 'together/with' and 'cavus' meant 'hollow'.

'double' came into English via Old French 'double' from Latin 'duplus'; 'concave' comes from Latin 'concavus' and entered English through Medieval Latin and Old French forms, eventually forming the compound adjective 'double-concave' in modern technical usage.

Initially the roots described 'twofold' and 'hollow' respectively; over time the compound came to mean specifically 'having two concave surfaces' as used in optics and geometry.