millstone vs baulk

millstone and baulk both are nouns.

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

As nouns, baulk is a hypernym of millstone; that is, baulk is a word with a broader meaning than millstone:

millstone: (figurative) something that hinders or handicaps
baulk: something immaterial that interferes with or delays action or progress

Other hypernyms of millstone include balk, check, deterrent, handicap, hinderance, hindrance, impediment.

millstone (noun)	baulk (noun)
one of a pair of heavy flat disk-shaped stones that are rotated against one another to grind the grain	one of several parallel sloping beams that support a roof
any load that is difficult to carry	something immaterial that interferes with or delays action or progress
(figurative) something that hinders or handicaps	the area on a billiard table behind the balkline

millstone (verb)	baulk (verb)
	refuse to comply