lake vs tarn

lake and tarn both are nouns.

Word	Noun	Adjective	Verb	Adverb
lake	Yes	No	No	No
tarn	Yes	No	No	No

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

lake (noun)	tarn (noun)
a body of (usually fresh) water surrounded by land	a mountain lake (especially one formed by glaciers)
any of numerous bright translucent organic pigments
a purplish red pigment prepared from lac or cochineal