Open English Wordnet
Adjectives
(s)firm, steadfast, steady, stiff, unbendable, unfaltering, unshakable, unwaveringmarked by firm determination or resolution; not shakable“firm convictions”, “a firm mouth”, “steadfast resolve”, “a man of unbendable perseverance”, “unwavering loyalty”
(s)steadfast, staunch, unswervingfirm and dependable especially in loyalty“a steadfast ally”, “a staunch defender of free speech”, “unswerving devotion”, “unswerving allegiance”