Lewis & Short

Vertumnus (Vort-), i, m. [qs. vertomenos, as a part. pass., from verto, that turns or changes himself], orig. an Etruscan deity, the god of the changing year, i. e. of the seasons and their productions, also of exchange and of trade, Varr. L. L. 5, § 46 Müll.; Prop. 4 (5), 2, 10; Ov. F. 6, 410; id. M. 14, 642 sq.; Cic. Verr. 2, 1, 59, § 154 Ascon. Near his statue in the forum at Rome were the booksellers’ shops, Hor. Ep. 1, 20, 1; also the market-gardeners, Col. poët. 10, 308.
As a symbol of mutability: Vertumnis natus iniquis, said of an unstable man, Hor. S. 2, 7, 14.
Hence, Vertum-nālĭa, ĭum, n., the festival of Vertumnus, Varr. L. L. 6, § 21 Müll.