Weapons are often a defence against fears of being hurt. If you shoot or stab someone or something, you need to consider what part of yourself you are turning your aggression upon. If you kill or injure a recognisable person, you may be harbouring the desire to hurt or kill that person, even if only in reputation.
Depending on how the knife appears in the dream, it can also mean cutting intellectual insight, aggression, or an attempt to wound someone. The knife is often an expression of aggressive male sexuality. Or maybe sexual feelings that have been damaged and express as aggression rather than love.
The situation in which the action takes place: Defines what the weapon expresses. Ineffective weapons: Feelings of inadequacy.
Idioms: Get one’s knife into someone; on a knife edge; under the knife – surgery; cut it out; cut the air with a knife.