Enter a clue or pattern or both:
The Clue
Toughening (7 letter answer)
The Answer
INURING
Tags
Notes
The answer INURING is so rare that it appears less than once every 2500 puzzles.
Definition
INURE as a verb:
1. (inure, harden, indurate) = cause to accept or become hardened to; habituate; "He was inured to the cold"