— ad-libber , n.
/ad lib", ad"-/ , v. , ad-libbed, ad-libbing , adj.
v.t.
1. to improvise all or part of (a speech, a piece of music, etc.): to ad-lib one's lines.
v.i.
2. to act, speak, etc., without preparation: Throughout the play he had to ad-lib constantly.
adj.
3. impromptu; extemporaneous: ad-lib remarks to hecklers.
[ 1915-20, Amer.; v. use of AD LIB ]