- Immune
- Impervious
- Impervious, unyielding
- Opposed (to)
- Opposed to relocating Iran tests
- Tough
- Unsusceptible (to)
- Cynical and difficult. Nipped ten
- Tough
- Unsentimental
- Difficult, at end of day, to be robust
- Resilient
- Rugged
- Slapstick comedy duo, Laurel and ...
- Sturdy
- Tough
- Bold; brave; stout; daring; resolu?e; intrepid.
- Animatedly
- Arduous
- Difficult
- industriously
- Male red deer
- Not easy
- Rigid
- Hardened (skin)
- Tough
- Tough (skin)
- Tough and flexible
- Resembling leather in appearance or consistence; tough.