Rigid
Hard
Synonyms Stiff, firm, non-flexible, unyielding, taut, impliable, hard, inflexible, unbending, inelastic, tight, and unmalleable.
Inflexible
Synonyms Fixed, firm, unalterable, immutable, invariable, cast-iron, set, inflexible, unchangeable, unvarying, and hard and fast.
Stringent
Synonyms Strict, stern, rigorous, uncompromising, determined, unshakeable, intransigent, unwavering, obdurate, adamant, severe, stringent, inflexible, resolute, immovable, unrelenting, unyielding, unswerving, and unadaptable.
Example Sentences
The structure was surprisingly rigid and strong.
His beliefs are quite rigid and inflexible.
The plastic became rigid when cooled.
She followed a rigid daily schedule.