Lewis & Short

rĭgor, ōris, m. [rigeo], stiffness, inflexibility, rigidity, numbness, hardness, firmness, rigor (not freq. till after the Aug. per.; not in Cic.; cf. durities).

  1. I. Lit.: tandem bruma nives affert pigrumque rigorem, Lucr. 5, 746: cervicis, stiffness, rigidity, Plin. 28, 12, 52, § 192; 32, 8, 28, § 89; cf.: immobilis faciei, Quint. 9, 3, 101: vultus (in portraits), Plin. 35, 9, 35, § 58: nervorum, i. e. a cramp, spasm, Cels. 2, 1 and 7; so too simply rigor; and in plur., Plin. 26, 12, 81, § 130; 35, 6, 27, § 46.
    1. B. Esp.
      1. 1. A straight course or direction: fluminis, Dig. 43, 12, 1, § 5; cf. stillicidii, ib. 8, 2, 41; hence, in the agrimensores, a straight line or course (opp. flexus), Front. Expos. Form. p. 38 Goes.; Aggen. Limit. p. 46 fin.; Sicul. Fl. p. 5; Front. Colon. p. 120 al.
      2. 2. Hardness, firmness: auri, Lucr. 1, 492: ferri, Verg. G. 1, 143: saxorum, Ov. M. 1, 401 (with durities): lapidis, Plin. 36, 16, 25, § 126: arborum, Vitr. 2, 9; Plin. 16, 40, 77, § 209; Col. 4, 16, 4 al.
  2. II. Transf., the stiffness produced by cold, for cold itself, chilliness, Lucr. 5, 640; 6, 368 (opp. calor); 307 (opp. ignis); cf. Alpinus, Ov. M. 14, 794: septentrionis, Tac. A. 2, 23: caeli et soli, Plin. 17, 24, 37, § 217: recentissimus aquae, Col. 9, 14, 7: torpentibus rigore nervis, Liv. 21, 58 fin. et saep.
  3. III. Trop., hardness, inflexibility, stiffness, roughness, severity, rigor (cf.: severitas, asperitas, morositas): accentus rigore quodam minus suaves habemus, Quint. 12, 10, 33 (cf. rigidus, II. init.): te tuus iste rigor, positique sine arte capilli … decet, rudeness, Ov. H. 4, 77: nocuit antiquus rigor et nimia severitas, Tac. H. 1, 18 fin.: animi, id. A. 6, 50; cf. Plin. 7, 19, 18, § 79; Sen. Ira, 1, 16, 13 (opp. constantia): disciplinae veteris, Tac. H. 1, 83: juris, Dig. 49, 1, 19.