unconventional vs improper

unconventional and improper both are adjectives.

Word	Noun	Adjective	Verb	Adverb
unconventional	No	Yes	No	No
improper	No	Yes	No	No

As adjectives, unconventional and improper are synonyms defined as:

unconventional and improper: not conforming to legality, moral law, or social convention

Other synonyms of unconventional include unlawful.

unconventional (adjective)	improper (adjective)
not conforming to accepted rules or standards	not suitable or right or appropriate
not conventional or conformist	not appropriate for a purpose or occasion
not conforming to legality, moral law, or social convention	not conforming to legality, moral law, or social convention