Lewis & Short

in-flexĭbĭlis, e, adj., that cannot be bent, inflexible.

  1. I. Lit.: dolor (cervicum), lockjaw = opisthotonos, Plin. 28, 12, 52, § 192; cf. Cael. Aur. Acut. 3, 6, 65.
  2. II. Transf.: judicium, unchangeable, Sen. Ep. 95: obstinatio, Plin. Ep. 10, 97, 3.