extemporaneously
extemporarily
extempore
without prior preparation
he spoke extemporaneously
ad-lib
extemporaneous
extemporary
impromptu
offhand
offhanded
off-the-cuff
unrehearsed
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