Antonyms for intentional

deliberate:

accidental, unintentional, unwilling, unplanned, involuntary.

noun:

compulsory, impulsive, necessary, forced, abrupt, ordered, haphazard, extemporaneous, desultory, unintended, purposeless, sudden, hit-or-miss, random, unforced, required, mandatory, obligatory, impetuous, nonelective, aimless.