SPI'RAL, adjective [Latin spira, a spire.] Winding round a cylinder or other round body, or in a circular form, and at the same time rising or advancing forward; winding like a screw. The magnificent column in the Place Vendeme, at Paris, is divided by a spiral line into compartments. It is formed with spiral compartments, on which are engraved figures emblematical of the victories of the French armies. A whirlwind is so named from the spiral motion of the air. Water in a tunnel descends in a spiral form.