Adjectives

(a)inflexibleincapable of change“a man of inflexible purpose”
(a)uncompromising, sturdy, inflexiblenot making concessions“took an uncompromising stance in the peace talks”, “uncompromising honesty”
(a)inflexibleresistant to being bent“an inflexible iron bar”, “an inflexible knife blade”
(s)inflexible, rigid, unbendingincapable of adapting or changing to meet circumstances“a rigid disciplinarian”, “an inflexible law”, “an unbending will to dominate”