unpremeditated (adj.)

• ad-lib
• advanced
• automatic
• casual
• coincidental
• extemporaneous
• extemporary
• extempore
• forward
• half-baked
• haphazard
• hasty
• ill-advised
• ill-considered
• impromptu
• improvised
• impulsive
• inadvertent
• involuntary
• last-minute
• makeshift
• natural
• offhand
• overhasty
• precipitate
• precocious
• premature
• previous
• reflex
• reflexive
• rough-and-ready
• rushed
• spontaneous
• spur-of-the-moment
• surprised
• unadvised
• unconscious
• unconsidered
• uncontrived
• uncrystallized
• undesigned
• unguarded
• unguided
• unhatched
• unintended
• unintentional
• unmade
• unorganized
• unplanned
• unprepared
• unprompted
• unready
• unripe
• unstudied
• unthinking
• unthought
• unthought-of
• untimely
• unwilled
• unwitting