ad libitum (ad lib-i-t<<schwa>>m), adv.[Law Latin] At pleasure. • The modern term ad-lib
(adj. & vb.), borrowed from drama and music, is essentially the same; it means “at the performer’s
pleasure,” and allows the performer discretion in innovating a part impromptu.
“[B]ut in actions where the damages are precarious, being to be assessed ad libitum by a jury,
as in actions for words, ejectment, or trespass, it is very seldom possible for a plaintiff to swear to
the amount of his cause of action; and therefore no special bail is taken thereon ….” 3 William
Blackstone, Commentaries on the Laws of England 292 (1768). [Blacks Law 8th]