'single-payment' is a modern English compound formed from 'single' and 'payment'. 'single' originates from Old French 'sengle' and ultimately Latin 'singulus', where 'singulus' meant 'one, individual'. 'payment' originates from Old French 'paiement' (Middle English 'payement'), from Latin 'pagare', where 'pagare' meant 'to pay (to settle a payment)'.

'single-payment' developed in modern English as a compound of the adjective 'single' and the noun 'payment'; the noun 'payment' came into English via Old French 'paiement' (Middle English 'payement') from Latin 'pagare', while 'single' came via Old French from Latin 'singulus'.

Initially the elements meant 'one' ('single') and 'an act of paying' ('payment'); combined they have retained the straightforward meaning 'a single/one-time payment' and have not undergone major semantic shift.