obstacle vs obstruction

obstacle and obstruction both are nouns.

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

As nouns, obstruction is a hypernym of obstacle; that is, obstruction is a word with a broader meaning than obstacle:

obstacle: an obstruction that stands in the way (and must be removed or surmounted or circumvented)
obstruction: any structure that makes progress difficult

Other hypernyms of obstacle include impediment, impedimenta, obstructer, obstructor.

As nouns, obstacle and obstruction are synonyms defined as:

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

obstacle (noun)	obstruction (noun)
an obstruction that stands in the way (and must be removed or surmounted or circumvented)	getting in someone's way
something immaterial that stands in the way and must be circumvented or surmounted	the act of obstructing
	any structure that makes progress difficult
	something immaterial that stands in the way and must be circumvented or surmounted
	the physical condition of blocking or filling a passage with an obstruction