nitre vs nitrate

nitre and nitrate both are nouns.

Word	Noun	Adjective	Verb	Adverb
nitre	Yes	No	No	No
nitrate	Yes	No	Yes	No

As nouns, nitrate is a hypernym of nitre; that is, nitrate is a word with a broader meaning than nitre:

nitre: (KNO3) used especially as a fertilizer and explosive
nitrate: any compound containing the nitrate group (such as a salt or ester of nitric acid)

nitre (noun)	nitrate (noun)
(KNO3) used especially as a fertilizer and explosive	any compound containing the nitrate group (such as a salt or ester of nitric acid)

nitre (verb)	nitrate (verb)
	treat with nitric acid, so as to change an organic compound into a nitrate