The Collaborative International Dictionary of English v.0.48:
Curb \Curb\, n.
1. That which curbs, restrains, or subdues; a check or
hindrance; esp., a chain or strap attached to the upper
part of the branches of a bit, and capable of being drawn
tightly against the lower jaw of the horse.
He that before ran in the pastures wild
Felt the stiff curb control his angry jaws.
By these men, religion,that should be
The curb, is made the spur of tyranny. --Denham.
2. (Arch.) An assemblage of three or more pieces of timber,
or a metal member, forming a frame around an opening, and
serving to maintain the integrity of that opening; also, a
ring of stone serving a similar purpose, as at the eye of
3. A frame or wall round the mouth of a well; also, a frame
within a well to prevent the earth caving in.
4. A curbstone.
5. (Far.) A swelling on the back part of the hind leg of a
horse, just behind the lowest part of the hock joint,
generally causing lameness. --James Law.
Curb bit, a stiff bit having branches by which a leverage
is obtained upon the jaws of horse. --Knight.
Curb pins (Horology), the pins on the regulator which
restrain the hairspring.
Curb plate (Arch.), a plate serving the purpose of a curb.
Deck curb. See under Deck.