Arithmetic and Algebra, denotes any number or quantity that is incommensurable to unity: it is otherwise called an irrational number or quantity.

Surdastrum, the ancient name of a drum used as an accompaniment to a pastoral pipe in a dance which was supposed to have the virtue of rendering harmless the bite of the tarantula.

Surdy, a small uninhabited island in the Persian Gulf, situated to the south of Kishme. Lat. 25. 54. N.

Surf is a term used by seamen to express a peculiar swell and breaking of the sea upon the shore. It sometimes forms but a single range along the shore, and at others three or four behind one another, extending perhaps half a mile out to sea.