UNSWERVING
steadfast, staunch, unswerving
(adjective) firm and dependable especially in loyalty; “a steadfast ally”; “a staunch defender of free speech”; “unswerving devotion”; “unswerving allegiance”
undeviating, unswerving
(adjective) going directly ahead from one point to another without veering or turning aside; “some people see evolution as an undeviating upward march from simple organisms to the very complex”; “a straight and narrow tree-lined road unswerving across the lowlands”
Source: WordNet® 3.1
Etymology
Adjective
unswerving (comparative more unswerving, superlative most unswerving)
Not deviating; not yielding or straying or varying.
Source: Wiktionary