ill-mannered vs unmannered

ill-mannered and unmannered both are adjectives.

Word	Noun	Adjective	Verb	Adverb
ill-mannered	No	Yes	No	No
unmannered	No	Yes	No	No

As adjectives, ill-mannered and unmannered are synonyms defined as:

Other synonyms of ill-mannered include bad-mannered, rude, unmannerly.

ill-mannered (adjective)	unmannered (adjective)
socially incorrect in behavior	socially incorrect in behavior
	without artificiality; natural