'double-dealer' originates from Modern English, formed as a compound of 'double' and 'dealer'; 'double' comes via Old French 'double' from Latin 'duplus' where 'du-' meant 'two', and 'dealer' derives from 'deal' (Old English 'dǣlan') meaning 'to distribute'.

'double-dealer' developed from the earlier phrase 'double dealer' in Early Modern English and by later usage became hyphenated as 'double-dealer' to mark the compound meaning of a two-faced person.

Initially it could be understood more literally as 'one who deals in two ways' or 'one who deals twice', but over time it evolved into the figurative sense 'a deceitful, two-faced person.'