loo vs lavatory

loo and lavatory both are nouns.

Word	Noun	Adjective	Verb	Adverb
loo	Yes	No	No	No
lavatory	Yes	No	No	No

As nouns, lavatory is a hypernym of loo; that is, lavatory is a word with a broader meaning than loo:

Other hypernyms of loo include bathroom, can, john, lav, privy, toilet.

loo (noun)	lavatory (noun)
a toilet in Britain	a room or building equipped with one or more toilets
	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