unpremeditated

adjectives

not prepared or planned in advance
"asked an unpremeditated question"
is similar to
without apparent forethought or prompting or planning
"an unplanned economy"; "accepts an unplanned order"; "an unplanned pregnancy"; "unplanned remarks"
not premeditated
antonym
is similar to
without forethought
"letting him borrow her car was an impulsive act that she immediately regretted"
see also
without apparent forethought or prompting or planning
"an unplanned economy"; "accepts an unplanned order"; "an unplanned pregnancy"; "unplanned remarks"