noun

• (figurative) Something that checks or restrains; a restraint.
  "Even by theſe Men, Religion, that ſhould be / The curb, is made the ſpur to tyranny: / They with their double key of conſcience bind / The Subjects ſouls, and leave Kings unconfin'd; […]"
• (equestrianism) A riding or driving bit for a horse that has rein action which amplifies the pressure in the mouth by leverage advantage placing pressure on the poll via the crown piece of the bridle and chin groove via a curb chain.
  "He that before ran in the pastures wild / Felt the stiff curb controul his angry jaws."
• (Canada, US) A sidewalk, covered or partially enclosed, bordering the airport terminal road system with adjacent paved areas to permit vehicles to off-load or load passengers.

verb

• (transitive) To check, restrain or control.
  "Curb your dog"
• (transitive) To rein in.
• (transitive) To furnish with a curb, as a well; to restrain by a curb, as a bank of earth.
• (transitive, slang) Ellipsis of curb stomp.