- Stiff by Webster's
(superl.) Not natural and easy; formal; constrained; affected; starched; as, stiff behavior; a...
- Rigid by Webster's
(a.) Firm; stiff; unyielding; not pliant; not flexible.(a.) Hence, not lax or indulgent; severe;...
- Sturdy by Webster's
(superl.) Stiff; stout; strong; as, a sturdy oak.(superl.) Resolute, in a good sense; or firm,...
- rigid by WordNet
adjectiveIncapable of or resistant to bending.usage: "a rigid strip of metal"; "a...
- Tough by Webster's
(superl.) Severe; violent; as, a tough storm.(superl.) Not easily broken; able to endure hardship;...