45 entries under vigorous topic. ×

25
indefatigable(adjective, strong, tough, continue, fit)
25
tireless(adjective, strong, continue, firm, difficult)
20
untiring(adjective, strong, continue, firm, solid)
18
unfaltering(adjective, strong, firm, solid, energetic)
10
unwearied(adjective, strong, continue, firm, energetic)
9
energetic(adjective, determined, active, full)
8
inexhaustible(adjective, strong, continue, firm, energetic)
8
unremitting(adjective, strong, firm, energetic, determined)
7
industrious(adjective, strong, difficult, energetic, lively)
7
unflinching(adjective, set, strong, firm, energetic)
6
dynamic(adjective, strong, moving, lively, active)
6
pertinacious(adjective, strong, firm, energetic, determined)
4
patient(adjective, strong, firm, energetic, determined)
4
strong(adjective, sound, tough, fit, firm)
3
active(adjective, strong, difficult, energetic, lively)
3
stalwart(adjective, strong, sound, tough, fit)
2
kinetic(adjective, strong, moving, energetic, lively)
2
lively(adjective, strong, moving, active)
2
rugged(adjective, strong, sound, tough, fit)
2
spirited(adjective, strong, moving, lively, active)
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APASmart Define. (2015). unflagging thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/unflagging/thesaurus/synonyms
ChicagoSmart Define. 2015. "unflagging thesaurus" https://smartdefine.org/unflagging/thesaurus/synonyms (accessed September 24, 2026).
HarvardSmart Define 2015, unflagging thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/unflagging/thesaurus/synonyms>.
MLASmart Define. "unflagging thesaurus" 14 April 2015. Web. 24 September 2026. <https://smartdefine.org/unflagging/thesaurus/synonyms>