The definition of adamant is someone who will never change his mind, or something that will never be changed.
Incapable of being changed; unalterable:
Not yielding; inflexible:
Find another word for all-or-nothing. In this page you can discover 8 synonyms, antonyms, idiomatic expressions, and related words for all-or-nothing, like: adamant, firm, hard-line, inflexible, unbending, uncompromising, unyielding and all-or-none.