"steep slope," in northern England esp. "the sides of a hill," early 14c., from Scot., "slope, river bank," from O.N. bra "eyelash," cognate with O.E. bræw "eyelid," Ger. Braue "eyebrow" (see brow). "The word must have passed through the sense of 'eye-brow' to 'brow of a hill', supercilium (cf. OE. eaghill 'eye-hill'=eyebrow)" [OED].