pond vs millpond

pond and millpond both are nouns.

Word	Noun	Adjective	Verb	Adverb
pond	Yes	No	No	No
millpond	Yes	No	No	No

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

pond: a small lake
millpond: a pond formed by damming a stream to provide a head of water to turn a mill wheel

Other hyponyms of pond include fishpond, horsepond, mere, swimming hole, water hole.

pond (noun)	millpond (noun)
a small lake	a pond formed by damming a stream to provide a head of water to turn a mill wheel