weir vs dam

weir and dam both are nouns.

Word	Noun	Adjective	Verb	Adverb
weir	Yes	No	No	No
dam	Yes	No	Yes	No

As nouns, dam is a hypernym of weir; that is, dam is a word with a broader meaning than weir:

weir: a low dam built across a stream to raise its level or divert its flow
dam: a barrier constructed to contain the flow of water or to keep out the sea

Other hypernyms of weir include dike, dyke.

weir (noun)	dam (noun)
a low dam built across a stream to raise its level or divert its flow	female parent of an animal especially domestic livestock
a fence or wattle built across a stream to catch or retain fish	a barrier constructed to contain the flow of water or to keep out the sea
	a metric unit of length equal to ten meters

weir (verb)	dam (verb)
	obstruct with, or as if with, a dam