n. See fool's cap, under fool.n. A writing-paper, usually folded, varying in size from 12 × 15 to 12½ × 16 inches: so called from its former watermark, the outline of a fool's head and cap, for which other devices are now substituted.n. A bivalve mollusk, Isocardia cor, better known as heart-shell.Of the size known as foolscap.