From Destinypedia, the Destiny wiki
The Hunter Knife is a multipurpose combat knife utilized by Guardians of the Hunter class. It is a utilitarian melee weapon, designed to ensure versatility in close-quarters combat. Hunters are capable of using the knife to silently eliminate their targets.
In the Gunslinger subclass, the knife doubles as a throwing knife. It can be thrown at enemies when its melee timer is fully charged; otherwise, the player will just stab with the knife. In the Bladedancer subclass, the knife is used as part of the Arc Blade super by being infused with Arc Light.
List of appearances