20
reliable(adjective, honest, solid, certain, true)
18
infallible(adjective, certain, sure, flawless, reliable)
17
loyal(adjective, good, strong, honest, solid)
16
constant(adjective, good, change, strong, continue)
16
sure(adjective, certain, true, definite, reliable)
15
certain(adjective, strong, certain, true, sure)
15
unflagging(adjective, strong, continue, firm, certain)
14
dependable(adjective, good, strong, honest, solid)
14
persistent(adjective, strong, continue, firm, certain)
14
trustworthy(adjective, good, strong, honest, solid)
11
foolproof(adjective, infallible)
11
staunch(noun, adjective, good, strong, firm)
11
steadfast(adjective, good, strong, honest, solid)
11
unfaltering(adjective, set, clear, strong, firm)
10
indefatigable(adjective, set, strong, continue, firm)
10
invariable(adjective, change, certain, regular, fixed)
10
steady(adjective, good, strong, firm, honest)
10
tireless(adjective, set, strong, continue, firm)
10
trusty(adjective, good, strong, honest, solid)
10
untiring(adjective, continue, determined, tired, persevering)
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APASmart Define. (2016). Unfailing thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/unfailing/thesaurus/synonyms
ChicagoSmart Define. 2016. "Unfailing thesaurus" https://smartdefine.org/unfailing/thesaurus/synonyms (accessed September 21, 2026).
HarvardSmart Define 2016, Unfailing thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/unfailing/thesaurus/synonyms>.
MLASmart Define. "Unfailing thesaurus" 3 March 2016. Web. 21 September 2026. <https://smartdefine.org/unfailing/thesaurus/synonyms>