I've always heard it called semantic change. Edward Sapir wrote about drift in his Language but he was talking about the tendency of languages to start changing (semantically, morphologically, syntacticly) and then head in a certain direction (or a set of similar changes cross linguistically.

[Edited typo.]

Last edited by zmjezhd; 10/15/2005 1:01 PM.
Ceci n'est pas un seing.