smùrach

dross, peat dross, smùir, dust, a particle of dust, smùirnean, a mote; cf. Scottish smurach, peat dross, smore, smurr, a drizzling rain, Middle English smóre, dense smoke, English smother (= smorther), Old Dutch smoor. O'R. has smur from Sh., and K.Meyer translates Middle Irish smur-chimilt as "grind to dust".