Lewis & Short

per-cognosco, nōvi, nĭtum, 3, v. a., to become perfectly acquainted with: aliquem, Plaut. Truc. 1, 2, 50 (Speng. pergnovi).
Hence, percognĭtus, a, um, P. a., well known: lex naturae non ignota, etsi nondum percognita, Plin. 2, 45, 45, § 116: Germania, id. 4, 14, 28, § 98; 37, 3, 11, § 45.