left wing vs faction

left wing and faction both are nouns.

Word	Noun	Adjective	Verb	Adverb
left wing	Yes	No	No	No
faction	Yes	No	No	No

As nouns, faction is a hypernym of left wing; that is, faction is a word with a broader meaning than left wing:

left wing: those who support varying degrees of social or political or economic change designed to promote the public welfare
faction: a dissenting clique

Other hypernyms of left wing include sect.

left wing (noun)	faction (noun)
those who support varying degrees of social or political or economic change designed to promote the public welfare	a dissenting clique
	a clique (often secret) that seeks power usually through intrigue