Functional shift

Functional shift is a term used in linguistics to refer to the way an existing word can take on a new syntactic function. For example, the word like, formerly only used as a preposition in comparisons (as in "eats like a pig"), is now also used in the same way as the subordinating conjunction as in many dialects of English (as in "sounds like he means it"). The boundary between functional shift and conversion (the derivation of a new word from an existing word of identical form) is not well-defined.