unfailing Synonyms

unflagging foolproof trusty trustworthy true tireless timeless sure steady steadfast staunch stable resolute undying unwearying unwearied unfaltering surefire sure-fire inerrant unswerving unerring unwavering unfading unchanging untiring weariless reliable persistent everlasting eternal endless devoted dependable deadly continual constant changeless certain ceaseless boundless faithful firm perseverant perpetual permanent loyal invariable infallible inextinguishable