Prusik

A Prusik /ˈprʌsɪk/ is a friction hitch or knot used to attach a loop of cord around a rope, applied in climbing, canyoneering, mountaineering, caving, rope rescue, and by arborists. The term Prusik is a name for both the loops of cord and the hitch, and the verb is "to prusik". More casually, the term is used for any friction hitch or device that can grab a rope. The word is often misspelled as Prussik, Prussick or Prussic, as it is a homophone with the term prussic acid.