Lewis & Short

in-dēclīnābĭlis, e, adj., inflexible, unchangeable, only in a trop. sense (postAug.).

  1. I. In gen., of things: virtus animum rectum et indeclinabilem praestat, Sen. Ep. 66: justitia, id. ib. 74: series re rum, Gell. 6, 2.
    Of persons: judex, Amm. 25, 4; id. 18, 1.
  2. II. In gram.: nomen, indeclinable, Diom. pp. 288, 289 P.
    Hence, indēclīnābĭlĭter, adv., unchangeably, Aug. Civ. Dei, 9, 22 fin.