Extempore
WordNet
adjective
(1) 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"
adverb
(2) Without prior preparation
"He spoke extemporaneously"
WiktionaryText
Etymology
From + , ablative singular of