A weapon; especially an open razor used as a weapon.
Origin
1970s. Origin uncertain; perhaps shortened from Malcolm Fraser (or Frazer), presumed rhyming slang for ‘razor’, although this is otherwise unattested and no connection with any person of this name has been established.
malky2
/ˈmalki/
Scottishslang (chieflyGlasgow )
verb
[with object]To do violence to (a person), especially to wound with an open razor.