A fiador (//) term of Spanish colonial origin referring to a hackamore component used principally in the Americas. In English-speaking North America, the fiador is known principally as a type of throatlatch used on the bosal-style hackamore. Its purpose is to stabilize a heavy noseband or bosal and prevent the bridle from shifting. It is not used for tying the horse.
A fiador-like design and fiador knot is also used under the jaw on some rope halters, usually ending in a loop to which a lead rope can be attached. This, however, is not an independent "fiador", nor generally labeled as such; it is simply an integral part of the halter itself.
MillerRWwas invoked but never defined (see the help page).