Prepay is from the prefix pre- ('before, in advance', from Latin prae-) + pay (from Old French paier, from Latin pacare 'to appease, satisfy', from pax 'peace'). Important recorded forms include prae- (Latin), pacare (Latin), and pax (Latin). Morphologically, the word preserves a built structure whose named elements carry the historical sense into English. The modern sense remains close to that composition, with the parts narrowing into a single lexical item. In current use it covers to pay for something in advance. The wider family includes derived forms such as prepayment, prepaid, and prepayable and related words such as pay, payment, and payable.