pulley vs bollock

pulley and bollock both are nouns.

Word	Noun	Adjective	Verb	Adverb
pulley	Yes	No	No	No
bollock	Yes	No	No	No

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

pulley: a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope
bollock: a pulley-block at the head of a topmast

Other hyponyms of pulley include bullock block, fairlead, idle pulley, idle wheel, idler pulley.

pulley (noun)	bollock (noun)
a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope	a pulley-block at the head of a topmast
	one of the two male reproductive glands that produce spermatozoa and secrete androgens