obstruction vs snag

obstruction and snag both are nouns.

Word	Noun	Adjective	Verb	Adverb
obstruction	Yes	No	No	No
snag	Yes	No	Yes	No

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

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

Other hyponyms of obstruction include barrier, roadblock, hang-up, hitch, rub, hurdle, stymie, stymy.

obstruction (noun)	snag (noun)
getting in someone's way	an unforeseen obstacle
the act of obstructing	an opening made forcibly as by pulling apart
any structure that makes progress difficult	a dead tree that is still standing, usually in an undisturbed forest
something immaterial that stands in the way and must be circumvented or surmounted	a sharp protuberance
the physical condition of blocking or filling a passage with an obstruction

obstruction (verb)	snag (verb)
	catch on a snag
	hew jaggedly
	get by acting quickly and smartly