(covers information from several alternate timelines)
A dagger is a small hand-held blade weapon.
Every Tamarian encountered by the crew of the USS Enterprise-D in 2368 owned a dagger, including their captain Dathon. After the death of the Tamarian captain the Tamarian officers performed a mourning ritual using their daggers. (TNG: "Darmok")
The same year, the Bajoran Sirah apprentice Hovath used a Bajoran dagger when he tried to kill Miles O'Brien because of his jealousy. O'Brien and Julian Bashir were able to disarm him. (DS9: "The Storyteller")
Terrans of the mirror universe used a dagger impaling the Earth as the symbol of their empire. Starfleet officer uniforms also had a dagger as standard accessory for over a hundred years. (ENT: "In a Mirror, Darkly"; TOS: "Mirror, Mirror")