Hessian

A Hessian is a native of Hesse, a region in central Germany, or something relating to that place.

Historically, Hessian soldiers were German mercenaries hired by the British to fight in the American Revolutionary War, making the term sometimes carry connotations of a hired fighter with no stake in the cause: Washington's troops captured nearly a thousand Hessians at Trenton.

In mathematics, a Hessian matrix contains second-order partial derivatives of a function, named after German mathematician Otto Hesse. (Lowercase hessian is the coarse fabric.)