UNGRAMMATICAL
ungrammatical, ill-formed
(adjective) not grammatical; not conforming to the rules of grammar or accepted usage
Source: WordNet® 3.1
Etymology
Adjective
ungrammatical (comparative more ungrammatical, superlative most ungrammatical)
(linguistics) In violation of one or more of the rules and conventions of a language as defined by the grammar, resulting in unacceptable or incorrect usage.
Usage notes
In formal linguistics, ungrammatical sentences are labelled using an asterisk (*)
*The subject of this sentence is.
This convention goes back at least as far as Leonard Bloomfield's Language (1933).
Synonyms
• agrammatical
• ungrammatic
Antonyms
• grammatical
Source: Wiktionary