RhymeZone: holdback definitions

Definitions of holdback:

noun: restraint (act or result of holding back, device that restrains)
noun: The projection or loop, on the thill of a vehicle, to which a strap of the harness is attached, to hold back a carriage when going downhill, or in backing.
noun: The strap or part of the harness so used.

(Definitions from Wiktionary)