lavatory vs flush toilet

lavatory and flush toilet both are nouns.

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

As nouns, lavatory and flush toilet are synonyms defined as:

lavatory and flush toilet: a toilet that is cleaned of waste by the flow of water through it

lavatory (noun)	flush toilet (noun)
a room or building equipped with one or more toilets	a toilet that is cleaned of waste by the flow of water through it
a bathroom sink that is permanently installed and connected to a water supply and drainpipe; where you can wash your hands and face
a toilet that is cleaned of waste by the flow of water through it