Lewis & Short

sordesco, dŭi, 3,

  1. I. v. inch. n. [sordeo], to become dirty, grow filthy (not ante-Aug., and very rare): contrectatus ubi manibus sordescere vulgi Coeperis (liber), * Hor. Ep 1, 20, 11: mel, Plin. 11, 12, 12, § 31: manus, id. 33, 3, 19, § 60: ager, i. e. to become wild, lie untilled, Gell. 4, 12, 1.
  2. II. Trop., to be mean, vile, Amm. 15, 13, 2.