unfailing
1 bottomless, boundless, ceaseless, continual, continuous, endless, inexhaustible, never-failing, persistent, unflagging, unlimited
2 certain, constant, dependable, faithful, infallible, loyal, reliable, staunch, steadfast, sure, tried and true, true
Antonyms
2 disloyal, fallible, inconstant, uncertain, unfaithful, unreliable, unsure, untrustworthy