hair gel vs gel

hair gel and gel both are nouns.

Word	Noun	Adjective	Verb	Adverb
hair gel	Yes	No	No	No
gel	Yes	No	Yes	No

As nouns, hair gel and gel are synonyms defined as:

hair gel (noun)	gel (noun)
jellylike substance used in hair styling	a thin translucent membrane used over stage lights for color effects
	jellylike substance used in hair styling
	a colloid in a more solid form than a sol

hair gel (verb)	gel (verb)
	apply a styling gel to
	become a gel