broom-grass, in botany: A genus of the digynia order, belonging to the triandra clas of plants; ranking, in the natural method, under the 4th order, Gramina. The calyx is bivalved, having a partial spike, oblong and round, opposite grains, with an awn below the point of each outer valve. There are 24 species, eight of which are natives of Britain, viz. the secalinus or field broom-grass; the arvensis, or common broom-grass; the ciliatus, or tall broom-grass; the sterilis, or barren broom-grass; the giganteus, or tall broom-grass; the ramulosus, or wood broom-grass; and the pinnatus, or spiked broom-grass.