Lewis & Short

Petrēĭus, i, m., name of a Roman gens.
So, esp, a lieutenant of Pompey in the civil war, Caes. B. C. 1, 38; 63; cf. Cic. Att. 8, 2, 3. He is probably the same person with M. Petrejus, lieutenant of the consul C. Antonius, who defeated the followers of Catiline at Fœsulœ, A. U. C. 692; Cic. Sest. 5, 12; Sall. C. 59, 5 sq.
Hence,

  1. A. Petrēius, a, um, adj., Petreian; here prob. belongs: petreia vocabatur, quae pompam praecedens in coloniis aut municipiis imitabatur anum ebriam, ab agri vitio, scilicet petris, appellata, Paul. ex Fest. p. 243, 5 Müll.; cf. Fest. p. 242, 14 ib.
  2. B. Petrēiānus, a, um, adj., of or belonging to Petreius, Petreian: auxilium, Auct. B. Afr. 19.