'saltwater-resistant' originates from modern English, specifically the compound of 'saltwater' and 'resistant' (where 'saltwater' is 'salt' + 'water' and 'resistant' comes from Latin roots meaning 'to stand back/against').

'salt' originates from Old English 'sealt' and 'water' from Old English 'wæter', forming the compound 'saltwater' in modern English. 'Resistant' derives from Latin 'resistere' (to stand back/against) via Old French and Middle English forms, giving modern English 'resistant'; together they formed the compound adjective 'saltwater-resistant'.

Initially, 'resistant' meant 'able to stand back or oppose' (from Latin), and 'saltwater' simply meant 'water containing salt'; over time the compound came to specifically mean 'able to resist damage or corrosion caused by saltwater'.