lake vs lough

lake and lough both are nouns.

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

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

lake (noun)	lough (noun)
a body of (usually fresh) water surrounded by land	Irish word for a lake
any of numerous bright translucent organic pigments	a long narrow (nearly landlocked) cove in Ireland
a purplish red pigment prepared from lac or cochineal