ill-formed vs ungrammatical

ill-formed and ungrammatical both are adjectives.

Word	Noun	Adjective	Verb	Adverb
ill-formed	No	Yes	No	No
ungrammatical	No	Yes	No	No

As adjectives, ill-formed and ungrammatical are synonyms defined as:

ill-formed and ungrammatical: not grammatical; not conforming to the rules of grammar or accepted usage

ill-formed (adjective)	ungrammatical (adjective)
not grammatical; not conforming to the rules of grammar or accepted usage	not grammatical; not conforming to the rules of grammar or accepted usage