caustic vs lye

caustic and lye both are nouns.

Word	Noun	Adjective	Verb	Adverb
caustic	Yes	Yes	No	No
lye	Yes	No	No	No

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

Other hyponyms of caustic include silver nitrate.

caustic (noun)	lye (noun)
the envelope of light rays reflected or refracted by a curved surface or object	a strong solution of sodium or potassium hydroxide
any chemical substance that burns or destroys living tissue

caustic (adjective)	lye (adjective)
of a substance, especially a strong acid; capable of destroying or eating away by chemical action
harsh or corrosive in tone