Mid 17th century (denoting a raised border or frame): variant of curb.

• curb from Late Middle English:

  A curb was a strap passing under the jaw of a horse and fastened to the bit, used for checking an unruly horse. This caused the horse to bend its neck, an action that produced the word. It derives from Old French courber ‘to bend or bow’, from Latin curvare, also the source of curve (Late Middle English). The idea of ‘holding back’ led to the more general sense of a check or restraint. Curb is also the American spelling of what in British English is a kerb (mid 17th century), a stone edging to a pavement or path. The original idea here was of a border or frame bending round something, for example, the top of a well or a trapdoor.