notion vs concept

notion and concept both are nouns.

Word	Noun	Adjective	Verb	Adverb
notion	Yes	No	No	No
concept	Yes	No	No	No

As nouns, concept is a hypernym of notion; that is, concept is a word with a broader meaning than notion:

notion: a general inclusive concept
concept: an abstract or general idea inferred or derived from specific instances

Other hypernyms of notion include conception, construct.

notion (noun)	concept (noun)
(usually plural) small personal articles or clothing or sewing items	an abstract or general idea inferred or derived from specific instances
a general inclusive concept
an odd or fanciful or capricious idea
a vague idea in which some confidence is placed