Usil is the Etruscan god of the sun. His iconic depiction features Usil rising out of the sea, with a fireball in either outstretched hand, on an engraved Etruscan bronze mirror in late Archaic style, formerly on the Roman antiquities market. On Etruscan mirrors in the Classical style, Usil appears with an aureole.

Usil was identified with the Roman Sol and Greek Helios. However, while Usil is depicted as male in some artwork, there are also feminine depictions. There is also a connection with the indigenous Etruscan goddess Catha, who has been interpreted as having a solar character, however she has also been identified with a Lunar character. In artwork, Usil is shown in close association with the dawn goddess Thesan, something almost never seen with Helios and Eos.

Catha has been identified as "Solis Filia" meaning "Sun's Daughter", making Usil her father.

Since his name appears on the bronze liver of Piacenza, next to Tiur, meaning both "moon" and "month", since then Tiur has been identified as the name of the personification of the moon, but it was most likely a date. The inscriptions on the Pyrgi Tablets confirm that "tiur" was meant as "month" for datations,.