"steep slope," in northern England esp. "the sides of a hill," 1330, from Scot., "slope, river bank," from O.N. bra "eyelash." "The word must have passed through the sense of 'eye-brow' to 'brow of a hill', supercilium (cf. OE. eaghill 'eye-hill'=eyebrow)" [OED].
[brey, bree; Scot. brey, bree] 
