Lewis & Short

pĕremnis, e, adj. [per-amnis], of or belonging to crossing a river; only in augural lang., peremne auspicium, and subst., pĕremne, is, n., the auspices taken by magistrates on crossing a river or a spring: peremne dicitur auspicari, qui amnem aut aquam, quae ex sacro oritur, auspicato transit, Fest. p. 245 Müll.; p. 250 Müll.: bella nullis auspiciis administrantur: nulla peremnia servantur, nulla ex acuminibus, Cic. N. D. 2, 3, 9; cf. id. Div. 2, 36, 77.