'frequency-independent' is a modern English compound formed from 'frequency' + 'independent'. 'frequency' comes from Latin 'frequentia' (via Old French/Medieval Latin) where it related to 'crowding' or 'repetition', and 'independent' comes from Latin 'independens' (in- 'not' + dependere 'to hang from').

'frequency' entered English via Middle French/Latin as 'frequentia' and developed the scientific sense 'rate of repetition' in the 18th–19th centuries. 'independent' arrived from Latin 'independens' through Middle English. The compound 'frequency-independent' arose in modern technical usage (20th century) to describe properties that do not change with frequency.

Originally 'frequency' referred to repetition rate and 'independent' simply meant 'not dependent on'. Over time, the compound came to mean specifically 'not changing as frequency changes' in scientific and engineering contexts.