Lewis & Short

callum, i, n. (callus, i, m., Cels. 5, 18, 36; 5, 26, 31 al.; Domit. Mars. ap. Charis. p. 55; plur. calli, Scrib. Comp. 37; 205; Suet. Aug. 80) [cf. Gr. καλάμη; Lat. culmus, culmen].

  1. I. The hardened, thick skin upon animal bodies: fere res omnes aut corio sunt Aut etiam conchis aut callo aut cortice tectae, Lucr. 4, 935: calceamentum solorum callum, Cic. Tusc. 5, 32, 90: pedum, Plin. 22, 25, 60, § 127; cf. id. 9, 35, 54, § 108.
    Plur., Suet. Aug. 80.
    Hence,
    1. B. Meton.
      1. 1. The hard flesh of certain animals: aprugnum, Plaut. Poen. 3, 2, 2; id. Pers. 2, 5, 4; for which absol. callum, id. Capt. 4, 3, 4; id. Ps. 1, 2, 33: manus elephanti, Plin. 8, 10, 10, § 31: locustarum, id. 9, 30, 50, § 95.
      2. 2. The hard skin or the hard flesh of plants: uvarum, Plin. 14, 1, 3, § 14: pirorum ac malorum, id. 15, 28, 34, § 116: fungorum, id. 22, 23, 47, § 96: foliorum, id. 16, 22, 34, § 82; Pall. Mart. 10, 28 al.
      3. 3. The hard covering of the soil: terrae, Plin. 17, 5, 3, § 33; 19, 2, 11, § 33; 31, 4, 30, § 53; also, of the hardness of salt: salis, id. 16, 12, 23, § 56.
  2. II. Trop., hardness, callousness, insensibility, stupidity (rare; most freq. in Cic.): ipse labor quasi callum quoddam obducit dolori, renders callous to pain, Cic. Tusc. 2, 15, 36; 3, 22, 53; id. Fam. 9, 2, 3: ducere, Sen. Cons. ad Marc. 8, 2: inducere, Quint. 12, 6, 6.