obstacle vs rub

obstacle and rub both are nouns.

Word	Noun	Adjective	Verb	Adverb
obstacle	Yes	No	No	No
rub	Yes	No	Yes	No

As nouns, rub is a hyponym of obstacle; that is, rub is a word with a more specific, narrower meaning than obstacle:

obstacle: something immaterial that stands in the way and must be circumvented or surmounted
rub: an unforeseen obstacle

Other hyponyms of obstacle include barrier, roadblock, hang-up, hitch, snag, hurdle, stymie, stymy.

obstacle (noun)	rub (noun)
an obstruction that stands in the way (and must be removed or surmounted or circumvented)	the act of rubbing or wiping
something immaterial that stands in the way and must be circumvented or surmounted	an unforeseen obstacle

obstacle (verb)	rub (verb)
	move over something with pressure
	cause friction
	scrape or rub as if to relieve itching