Lewis & Short

in-frăgĭlis, e, adj., that cannot be broken to pieces.

  1. I. Lit.: adamas, Plin. H. N. 20 prooem. § 2.
  2. II. Trop., strong, that cannot be weakened: vox, Ov. Tr. 1, 5, 53: animi, Sen. Vit. B. 9.