Lewis & Short

cognōmentum, i, n. [access. form of cognomen],

  1. I. a surname (rare in class. prose; most freq. in Tac.; not used by Cic.; v. Madv. ad Cic. Fin. 2, 5, 15), Plaut. Mil. 4, 2, 47; id. Ps. 4, 2, 20; id. Pers. 1, 2, 8; Poët. ap. Cic. Fin. 2, 5, 15; Sall. Fragm. ap. Gell. 18, 4, 4; Messala ap. Sen. Suas. 2; Tac. A. 12, 55; 14, 27; Gell. 18, 7, 1.
  2. II. (Like cognomen in poets, v. cognomen, II.) In gen., a name (partic. of inanim. things or of persons to designate a peculiar quality), Tac. A. 1, 31 Nipperd.; 2, 6; 2, 60; 4, 65; 11, 11; 15, 40; id. H. 5, 2.