If you use the knife as the weapon in order to protect yourself, it means that you feel as being attacked by something or someone. You know that there is no one that can protect you, but yourself. The knife thats been used against you indicates the dangers you could put yourself into. The dream suggests to be more careful with people you know.
Dream dictionary: knife as a weapon dream meanings
Dreaming of one or more knives or any other white and light weapon announces the presence of hidden but dangerous enemies. If the weapon appears in the hands of someone who is acting in a threatening manner, it means that the dreamers enemies are willing to do the worst. If the dreamer snatches the knife from the other person it could mean that he or she will triumph over enemies and adversities in the immediate future.
…Dreaming of firearms (the bigger and powerful, the worse) means an alteration of the nervous system. Firearms in a dream foretell that the dreamer fears that new war or an attack occurs in his personal life. This dream is more common in young men who do not wish to participate in any war. Dreaming of small and commonly used weapons indicates fear of being assaulted or attacked by your enemies by surprise. When a woman dreams of weapons, particularly firearms, it suggests that somehow shes getting involved with military people. Weapons in general, indicate violence, brawls, quarrels, fights, unfair competition in the case of commerce, envy, jealousy and betrayal. Dreaming of being wounded by a knife indicates that someone is betraying the trust of the dreamer. If you have been shot to death by a gun in a dream, it can be severe sign and announce that someone close…