means A roller is a cylinder—of metal, rubber, wood, or hair—that turns on an axis to flatten, move, spread, paint, or curl whatever it touches.

from From the verb 'roll,' which came through Old French 'roller' from Latin 'rotulare,' 'to turn like a wheel,' itself a diminutive of 'rota,' wheel. So at the root of every roller is the same little rotating thing that gave us 'rotate,' 'round,' and the 'rotunda'—a family of objects that get places by going in circles. The '-er' simply names the thing that does the rolling, the way a 'cutter' cuts and a 'mixer' mixes.