impermanent
temporary
ad hoc
ad libitum
ad-lib
band-aid
caught napping
caught off balance
caught short
extemporaneous
extemporary
extempore
extemporized
haphazard
hasty
impromptu
improvisational
improvisatorial
improvise
improviso
jury-rigged
makeshift
makeshifty
off-the-cuff
offhand
precipitate
provisional
rough-and-ready
snap
stopgap
surprised
taken aback
taken by surprise
taken unawares
tentative
tripped up
unarranged
unbegun
unconcocted
uncontrived
undeliberated
undevised
unhatched
unmade
unmanufactured
unorganized
unplanned
unpremeditated
unprepared
unprimed
unready