Lewis & Short

circĭus (cercĭus, Cato ap. Gell. 2, 22, 28 sq.), ii, m. [perh. from circus, on account of its circular motion, but said to be a Gallic word], a violent wind blowing in Gallia Narbonensis; to the Romans, a west-northwest wind, Plin. 2, 47, 46, § 121; Sen. Q. N. 5, 17, 5, Vitr. 1, 6, 10; Suet. Claud. 17; Favorin. ap. Gell. 2, 22, 20 sq.