1. with little or no preparation or forethought

e.g. his ad-lib comments showed poor judgment
an extemporaneous piano recital
an extemporary lecture
an extempore skit
an impromptu speech
offhand excuses
trying to sound offhanded and reassuring
an off-the-cuff toast
a few unrehearsed comments

Synonym: ad-libextemporaryextemporeimpromptuoffhandoffhandedoff-the-cuffunrehearsed