lye vs caustic potash

lye and caustic potash both are nouns.

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

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

Other hyponyms of lye include potash, potassium hydroxide, caustic soda, sodium hydroxide.

lye (noun)	caustic potash (noun)
a strong solution of sodium or potassium hydroxide	a potassium compound often used in agriculture and industry