Open English Wordnet
Adjectives
(s)ad-lib, extemporaneous, extemporary, extempore, impromptu, offhand, offhanded, off-the-cuff, unrehearsedwith little or no preparation or forethought“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”
Adverbs
(r)offhand, offhanded, offhandedlywithout previous thought or preparation“couldn't give the figures offhand”, “we decided offhand to go to Canada”, “she had made these remarks offhandedly”
(r)offhand, offhanded, offhandedlyin a casually inconsiderate manner“replied offhand, his mind a million miles away”, “she threw him over offhandedly without even a Dear-John letter”