Acorn, the corn or fruit of the oak (Anglo-Saxon ac), formed of three coherent carpels with an adherent perianth-tube, which terminates in a point and becomes horny. Its three chambers' and their six ovules are aborted to one chamber with generally but one seed. The acorn is surrounded at the base by a cup or cupule. The bitterness of the seed varies both in species and in individuals, the acorns of several kinds of evergreen oak being still used as human food in the Mediterranean region. Swine, deer and goats, squirrels, pigeons, and other animals feed largely upon acorns.