Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
The curb put into the mouths of horses to restrain them. The Hebrew word (metheg) so rendered in Ps. 32:9 is elsewhere translated "bridle" (2 Ki. 19:28; Pr. 26:3; Isa. 37:29). Bits were generally made of bronze or iron, but sometimes also of gold or silver. In Jas. 3:3 the Authorized Version translates the Greek word by "bits," but the Revised Version by "bridles."