Darsek

From Memory Alpha, the free Star Trek reference

The darsek is the main unit of currency in the Klingon Empire.

In 2153, the Tellarite bounty hunter Skalaar should have been paid 9,000 darseks for the delivery of the Human Jonathan Archer, but was later fleeced of 3,000 darseks. (ENT: "Bounty")

In 2370, on Maranga IV, Alexander Rozhenko asked his father Worf for 50 darseks to see the mummified head of Molor. (TNG: "Firstborn")