Princeton's WordNet

1. ad-lib, extemporaneous, extemporary, extempore, impromptu, offhand, offhanded, off-the-cuff, unrehearsed(adj)

   with 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"

2. offhand, offhanded(adverb)

   casually thoughtless or inconsiderate

   "an offhand manner"; "she treated most men with offhand contempt"

3. off-hand, ex tempore(adverb)

   without preparation

   "I don't know the figures off-hand"

4. offhand, offhanded, offhandedly(adverb)

   without previous thought or preparation

   "couldn't give the figures offhand"; "we decided offhand to go to Canada"; "she had made these remarks offhandedly"

5. offhand, offhanded, offhandedly(adverb)

   in a casually inconsiderate manner

   "replied offhand, his mind a million miles away"; "she threw him over offhandedly without even a Dear-John letter"