kiln vs furnace

kiln and furnace both are nouns.

Word	Noun	Adjective	Verb	Adverb
kiln	Yes	No	No	No
furnace	Yes	No	No	No

As nouns, furnace is a hypernym of kiln; that is, furnace is a word with a broader meaning than kiln:

kiln: a furnace for firing or burning or drying such things as porcelain or bricks
furnace: an enclosed chamber in which heat is produced to heat buildings, destroy refuse, smelt or refine ores, etc.

kiln (noun)	furnace (noun)
a furnace for firing or burning or drying such things as porcelain or bricks	an enclosed chamber in which heat is produced to heat buildings, destroy refuse, smelt or refine ores, etc.