The definition of adamant is someone who will never change his mind, or something that will never be changed.
Not yielding; inflexible:
Incapable of being changed; unalterable:
Find another word for all-or-nothing. In this page you can discover 9 synonyms, antonyms, idiomatic expressions, and related words for all-or-nothing, like: all-or-none, adamant, hard-line, unbending, inflexible, uncompromising, unyielding, either-or and firm.