edge vs knife edge

edge and knife edge both are nouns.

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

As nouns, knife edge is a hyponym of edge; that is, knife edge is a word with a more specific, narrower meaning than edge:

edge (noun)	knife edge (noun)
a sharp side formed by the intersection of two surfaces of an object	the sharp cutting side of the blade of a knife
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

edge (verb)	knife 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