ungrammatical

English Thesaurus

1. not grammatical; not conforming to the rules of grammar or accepted usage (adj.all)

similar	:	incorrect,
definition	:	(of a word or expression) not agreeing with grammatical principles (adj.all)

antonym	:	grammatical, well-formed,
definition	:	conforming to the rules of grammar or usage accepted by native speakers (adj.all)

antonym	:	grammatical, well-formed,
definition	:	conforming to the rules of grammar or usage accepted by native speakers (adj.all)