'constant-retardation' is a compound formed from English 'constant' and 'retardation'. 'constant' ultimately comes from Latin 'constans' (from 'constare'), where 'con-'/ 'com-' meant 'together'/'with' and 'stare' meant 'to stand'; 'retardation' comes from Latin 'retardatio', from 'retardare' meaning 'to make slow' ('re-' meaning 'back' + 'tardare' meaning 'to delay/slow').

'constant' entered English via Old French and Middle English from Latin 'constans'; 'retardation' developed from Latin 'retardatio' through French 'retardation' and entered modern English with the sense of 'the act of slowing'. Combining the two as a technical phrase (constant retardation) is an English-language compound used in physics to describe uniform slowing.

Individually, 'constant' originally meant 'standing firm' and 'retardation' meant 'the act of making slow'; together the compound came to denote the specific physical concept 'steady slowing' or 'constant deceleration'.