Real Dictionary

knife
countable noun: A knife is a tool for cutting or a weapon and consists of a flat piece of metal with a sharp edge on the end of a handle.
countable noun: A surgeon's knife is a piece of equipment used to cut flesh and organs during operations. It is made of metal and has a very thin sharp edge.
verb: To knife someone means to attack and injure them with a knife.

knife in American English
a cutting or stabbing instrument with a sharp blade, single-edged or double-edged, set in a handle
to cut or stab with a knife
to pass into or through something quickly, like a sharp knife
noun: an instrument for cutting, consisting essentially of a thin, sharp-edged, metal blade fitted with a handle

knife in British English
noun: a cutting instrument consisting of a sharp-edged often pointed blade of metal fitted into a handle or onto a machine

knife in Hospitality
noun: A knife is a tool for cutting and consists of a flat piece of metal with a sharp edge on the end of a handle.