'subsequentness' originates from Latin, specifically the word 'subsequens', where 'sub-' meant 'after' and 'sequi' meant 'to follow'; the suffix '-ness' comes from Old English '-nes(s)e', meaning a state or quality.

'subsequentness' developed from the Latin present participle 'subsequens' → Old French/Latin-influenced adjective 'subsequent' → Middle English 'subsequent', and in Modern English the noun form was created by adding the suffix '-ness' to form 'subsequentness'.

Initially it was associated with the adjective meaning 'following' (as in 'subsequent'); over time the derived noun came to mean specifically 'the state or quality of following'.