cutting edge vs knife edge

cutting edge and knife edge both are nouns.

Word	Noun	Adjective	Verb	Adverb
cutting edge	Yes	No	No	No
knife edge	Yes	No	No	No

As nouns, cutting edge and knife edge are synonyms defined as:

cutting edge and knife edge: the sharp cutting side of the blade of a knife

cutting edge (noun)	knife edge (noun)
the sharp cutting side of the blade of a knife	the sharp cutting side of the blade of a knife
the position of greatest importance or advancement; the leading position in any movement or field