Lewis & Short

firmĭtūdo, ĭnis, f. [firmus], firmness, durability, strength (less freq. than firmitas, but class.).

  1. I. Lit.: tanta in eis (navibus) erat firmitudo, Caes. B. G. 3, 13, 8; cf.: tanta erat operis (i. e. pontis) firmitudo, id. ib. 4, 17, 7: vocis, Auct. Her. 3, 11, 20.
  2. II. Trop., firmness, constancy, stability, strength of mind: animi, Plaut. As. 2, 2, 54; cf.: quod firmitudinem gravitatemque animi tui perspexi, Cic. Fam. 5, 13, 3: quantum esset hominibus praesidii in animi firmitudine, Caes. B. C. 3, 28, 4: animi, Tac. A. 4, 8: in patientia firmitudinem simulans, id. ib. 6, 46 fin.; cf. ib. 15, 62: non quod salus ab isto data quicquam habitura sit firmitudinis, Cic. Att. 11, 14, 2: haec constitutio habet firmitudinem, id. Rep. 1, 45: (translationes) per se minus habeant firmitudinis, id. Inv. 2, 19, 58.