Lewis & Short

impĕtrĭo, no perf., ītum, 4, v. n. desid. [id.], relig. t. t., to seek to obtain through omens, to seek by consulting auspices: ut nunc extis, sic tunc avibus magnae res impetriri solebant, Cic. Div. 1, 16, 28: in impetriendis consulendisque rebus, id. ib. 1, 2, 3: qui impetrire velit, id. ib. 2, 15, 35: impetritum, inauguratum est: quovis admittunt aves, Plaut. As. 2, 1, 11.
Part. as subst.: impetrītum, i, n., a favorable auspice or omen, Val. Max. 1, 1, 1; Plin. 28, 2, 3, § 11.