stool vs flush toilet

stool and flush toilet both are nouns.

Word	Noun	Adjective	Verb	Adverb
stool	Yes	No	Yes	No
flush toilet	Yes	No	No	No

As nouns, flush toilet is a hyponym of stool; that is, flush toilet is a word with a more specific, narrower meaning than stool:

stool: a plumbing fixture for defecation and urination
flush toilet: a toilet that is cleaned of waste by the flow of water through it

Other hyponyms of stool include flushless toilet, lavatory, potty chair, potty seat.

stool (noun)	flush toilet (noun)
a simple seat without a back or arms	a toilet that is cleaned of waste by the flow of water through it
a plumbing fixture for defecation and urination
(forestry) the stump of a tree that has been felled or headed for the production of saplings
solid excretory product evacuated from the bowels

stool (verb)	flush toilet (verb)
have a bowel movement
grow shoots in the form of stools or tillers
react to a decoy, of wildfowl
lure with a stool, as of wild fowl