Lewis & Short

Portūnus (less correctly Portum-nus), i, m. [portus],

  1. I. the protecting god of harbors, also called Palaemon, Cic. N. D. 2, 26, 66; Ov. F. 6, 547; Verg. A. 5, 241 Serv.; Lact. 1, 21, 23; Inscr. Orell. 1585; Paul. ex Fest. p. 243.
    Hence,
  2. II. Portūnālis (Portumn-), e, adj., of or belonging to Portunus, Portunal: flamen, Poët. ap. Fest. s. v. persillum, p. 217 Müll.
      1. 2. Subst.: Portūnālĭa, ĭum, n., the festival of Portunus, celebrated annually on the 17th of August, Varr. L. L. 6, § 19 Müll.; Calend. ap. Inscr. Orell. 2, p. 396.