The prefix ex- comes from Latin ex-, e-, meaning “out of, from.” It usually occurs with word roots that come from Latin verbs. Thus combining ex- with the Latin verb tendere, “to stretch,” gives us extend, “to stretch out.” Similarly, in express, ex- combines with the root press, which comes from the verb premere, “to squeeze.” So when we express ourselves, we “squeeze out” our thoughts. When followed by f, ex- becomes ef-, as in efface. Sometimes ex- takes the form of e-, as in emit (from Latin mittere, “to send"). Today ex- only forms new words when it means “former,” and it is always followed by a hyphen: ex-President.
