'hydrogen-deficient' is a modern English compound formed from 'hydrogen' and 'deficient'. 'hydrogen' originates from Greek elements 'hydro-' + 'genes', where 'hydro-' meant 'water' and '-genes' meant 'forming'. 'deficient' originates from Latin 'deficere'/'deficiens' meaning 'lacking' or 'failing'.

'hydrogen' was coined in New Latin/French as 'hydrogène' in the late 18th century (Lavoisier era) and entered English as 'hydrogen'; 'deficient' came from Latin 'deficiens' through Old French/Middle English and became modern English 'deficient'. The compound 'hydrogen-deficient' is a later, literal combination used in scientific contexts.

Initially the elements 'hydro-' and '-genes' named the gas that forms water; 'deficient' originally meant 'lacking' in a general sense. Combined as 'hydrogen-deficient', the phrase retained the literal meaning of 'lacking hydrogen' and became specialized for chemical descriptions.