bridle (n.)

"headpiece of a horse's harness," used to govern and restrain the animal, Old English bridel "a bridle, a restraint," related to bregdan "move quickly," from Proto-Germanic *bregdilaz (see braid (v.)). The etymological notion would be that which one "pulls quickly." Cognate with Old Frisian bridel, Middle Dutch breydel, Dutch breidel, Old High German bridel. A bridle-path (1806) is one wide enough to be traveled on horseback but not with a carriage.

"to control, dominate; restrain, guide, govern," c. 1200, a figurative use of Old English bridlian "to fit with a bridle," from bridel (see bridle (n.)). Meaning "to throw up the head" (as a horse does when reined in) is from mid-15c. Related: Bridled; bridling.