Functional linguists are in general agreement that semantic change may be triggered as part of the negotiation of meaning in interactional contexts: a ‘one-off’ contextual implicature generalises to become a new core meaning of a lexical item (Traugott and Dasher, 2002). In what ways, however, does the ‘one-off’ contextual implicature arise? Why would one language develop one aspect of meaning and another a different one? And how or why does it generalise and become a coded part of the structure of that particular language? Hansen (2008: 228) notes that “close crosslinguistic comparisons of the polysemies of semantically related items […] should turn out to be highly relevant” in this respect. ‘False friends’, forms deriving from a common etymon which have developed different meanings in different languages, offer useful insights. This paper presents lexicographic and spoken synchronic data on two false friends in French and English, effectivement/‘effectively’ and finalement/‘finally’, and explores the cognitive processes involved in their recruitment for interactional functions. The factors which are influential in the development of hedging usages of the terms are overviewed and the contribution that a detailed synchronic study of the semantics of false friends can make to the study of semantic change is evaluated.