Lewis & Short

per-nĕcessārĭus, a, um, adj.

  1. I. Very necessary: tempus, Cic. Att. 5, 21, 1: res, Dig. 4, 4, 11, § 4.
  2. II. Very closely connected with one: amicus, Cic. Fl. 6, 14: homo, id. de Or. 2, 50, 202; cf.: pro homine intimo ac mihi pernecessario, id. Fam. 13, 69.
    Subst.: meus familiaris et Leptae nostri familiarissimi pernecessarius, Cic. Fam. 9, 13, 1: meos, id. ib. 13, 40.