knife edge vs edge

knife edge and edge both are nouns.

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

As nouns, edge is a hypernym of knife edge; that is, edge is a word with a broader meaning than knife edge:

knife edge (noun)	edge (noun)
the sharp cutting side of the blade of a knife	a sharp side formed by the intersection of two surfaces of an object
	the outside limit of an object or area or surface; a place farthest away from the center of something
	a slight competitive advantage
	the attribute of urgency in tone of voice
	the boundary of a surface
	a line determining the limits of an area

knife edge (verb)	edge (verb)
	lie adjacent to another or share a boundary
	provide with an edge
	advance slowly, as if by inches
	provide with a border or edge