drain vs sewer

drain and sewer both are nouns.

Word	Noun	Adjective	Verb	Adverb
drain	Yes	No	Yes	No
sewer	Yes	No	No	No

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

Other hyponyms of drain include culvert, scupper, cloaca, sewerage, soil pipe, trap.

drain (noun)	sewer (noun)
emptying something accomplished by allowing liquid to run out of it	a waste pipe that carries away sewage or surface water
a gradual depletion of energy or resources	misfortune resulting in lost effort or money
a pipe through which liquid is carried away	someone who sews
tube inserted into a body cavity (as during surgery) to remove unwanted material

drain (verb)	sewer (verb)
empty of liquid; drain the liquid from
make weak
deplete of resources
flow off gradually