Coom :: Coom (n.) Soot; coal dust; refuse matter, as the dirty grease which comes from axle boxes, or the refuse at the mouth of an oven..
Coomb :: Coomb (n.) A dry measure of four bushels, or half a quarter..
Coombe :: Coombe (n.) A hollow in a hillside. [Prov. Eng.] See Comb, Combe..