What is the term for words that have changed meaning over time?

Snafu has not so much changed its meaning over time as come to be used by a larger linguistic community. Nevertheless, words do change their meaning over time. Where a word with a general meaning comes to have a more specific one, the process is semantic narrowing. An example is deer, which once meant any kind of animal, but now means only members of the family Cervidae. The opposite process is semantic widening. An example is office, which was limited to various ecclesiastical meanings before developing the uses which we know today.