baulk vs obstruction

baulk and obstruction both are nouns.

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

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

baulk: something immaterial that interferes with or delays action or progress
obstruction: something immaterial that stands in the way and must be circumvented or surmounted

Other hyponyms of baulk include albatross, millstone, bind, diriment impediment, drag, obstacle, straitjacket.

baulk (noun)	obstruction (noun)
one of several parallel sloping beams that support a roof	getting in someone's way
something immaterial that interferes with or delays action or progress	the act of obstructing
the area on a billiard table behind the balkline	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

baulk (verb)	obstruction (verb)
refuse to comply