in botany: A genus of the triandria digynia clasps; and in the natural method ranking under the 4th order, Gramina. The characters are: The calyx is a two-flowered double-valved glume: The corolla is two-valved, and no rudiment of a flower between the florets: The filaments consist of three capillary filaments the length of the flower; the anthers are oblong, and forked at both ends: The pistillum is an egg-shaped germen; the styli are two, briefly, and expanding; the stigmae are pubescent: There is no pericarpium; the including corolla grows to the seed: The seed is egg-shaped and covered. There are 14 species of the aira, nine of which are natives of Britain. The English name is Hair-grass. See the general article Grass.