Synonyms for On purpose:

adv

deliberately (adverb)
by design.

adv.

deliberately (adverb)
advisedly.
on purpose (adverb)
intentionally, deliberately, purposely, by design.
purposely (adverb)
designedly.

n.

on purpose (noun)
intentionally, deliberately, advisedly, designedly, purposely, by choice, by design.

Other synonyms:

Other relevant words:
deliberately.