n.
 (pl. knives)
 a cutting instrument consisting of a blade fixed into a handle. 
▸a cutting blade on a machine.
v.
  - stab with a knife.
- cut like a knife.
Phrase
  
    - before you can say knife
 informal very quickly.
- get 
(or stick)
 the knife into 
(or in)
 informal be malicious or vindictive towards.
- go 
(or be)
 under the knife
 informal have surgery.
 
  Derivative
  
    - knife-like adj.
- knifer n.
 
  Etymology
  OE cnīf, from ON knífr, of Gmc origin.