Neither rigid nor initially are synonyms for worse.
A synonym for changable is adaptable.
A synonym for common noun is word.
A synonym for debris is garbage. An antonym for debris is cleanliness.
detector or metal detectors
a synonym is like more than one word that means the same thing
rigid
one of them is stiff.
flexible, invariable, rigid
determined, fixed, rigid, set, firm
severe, rigid, bitter, rough
no
If you mean hard as in the opposite of soft, then rigid, firm, adamatine. If you mean the opposite of easy, then difficult
You could use fixed, rigid, solid, stiff, or tough as a synonym for unyielding.
antipathy, anger, cruelty, spite, rancor, rigor
Some synonyms for the verb stiffened are made rigid, firmed, fixed, hardened, petrified, reinforced, or tensed.
hard, strong, sturdy, tough, rugged, determined, resolute, unyielding, unbending, firm, rigid, unwavering
straight, upright, tough, disciplinary, harsh