Definition of adamant:

impervious to pleas, persuasion, requests, reason

Synonyms of adamant:

adamantine, inexorable, intransigent, stubborn, inflexible, unyielding, obdurate, rigid, unbending, uncompromising

Opposite/Antonyms of adamant:

flexible, yielding, pliant, soft, submissive, supple, receptive, compliant, tractable

Sentence/Example of adamant:

The eyes beneath the coifed brow with its fine network of wrinkles were adamant.