Synonyms for rigid

adamant, firm, hard, hard-line, harsh, immovable, immutable, industrious, inflexible, invariable, obstinate, overstrict, puritanical, relentless, rigorous, solid, stern, stiff, strait-laced, strict, stringent, stubborn, unadaptable, unbendable, unbending, uncompromising, undeviating, unrelenting, unwavering, unyielding