'paid-up' originates from English, combining the past participle 'paid' (from Old French 'paier' < Latin root often cited as 'pacare'/'pac-', via Vulgar Latin) and the adverb 'up' (Old English 'up').

'paid' developed as the past participle of Middle English 'paien'/'payen' (from Old French 'paier'); combined with the adverb 'up' (Old English 'up'), the compound 'paid up' was used in English and later hyphenated as 'paid-up' for adjectival use.

Initially it meant simply 'paid' or 'paid completely' (the combination emphasizing completion); over time it became a fixed adjectival form meaning 'fully paid' or 'paid in full'.