Lewis & Short

perpĕrus, a, um, adj., = πέρπερος (prop. heedless, inconsiderate; hence, in gen.), not properly constituted, faulty, defective, wrong (as adj. only ante- and postclass.): populares, Att. ap. Non. 150, 12: nihil perperum, Vop. Tac. 6 (dub.; al. praeproperum).
Hence, adv.

  1. A. perpĕram (adv. acc. fem. like clam, coram, palam; and in the plur. alias, alteras), wrongly, incorrectly, untruly, falsely (class.): loqui, Plaut. Am. 1, 1, 92: suadere aliquid, id. Capt. 2, 2, 78: insanire, id. Men. 5, 5, 59: dicere aliquid, Ter. Phorm. 5, 1, 18 (Serv. ad loc.): si aspires perperam, Nigid. ap. Gell. 13, 6, 3: seu recte, seu perperam fecerunt, Cic. Quint. 8, 31: recte an perperam judicare, id. Caecin. 24, 69: interpretari, Liv. 1, 23; Sen. Ep. 9, 13; Suet. Aug. 92: pronunciare, Plin. Ep. 3, 5, 12.
    1. 2. In a milder signif., erroneously, by mistake: ita dico, ne ad alias aedis perperam deveneris, Plaut. Most. 4, 2, 52; Varr. R. R. 1, 69, 2: perperam praeco non consulem, sed imperatorem pronunciavit, Suet. Dom. 10; Auct. B. Hisp. 12.
  2. B. perpĕrē, wrongly, falsely: opiniones perpere praesumptae, Claud. Mam. Stat. Anim. 1, 1.