tough cookie

noun3

1. •
   (informal) A person who can endure physical or mental hardship; a hardened, strong-willed person.

   • An austere, hard-lining rightist, who lives alone, Ioannidis is described by one Washington military official as "a real tough cookie." — 1973
2. •
   (informal) A hardy, resilient animal or plant.

   • Boxwood is a pretty tough cookie. Wind, cold, wet, exhaust fumes, and industrial pollution are of no consequence. — 2001
3. •
   (informal) Something troublesome or difficult to handle.

   • The pup that struggles constantly might be one tough cookie when it comes to training; […] — 2002