142 entries under firm topic. ×

12
sound(adjective, calm, strong, fit)
12
steadfast(adjective, calm, clear, strong, severe)
11
relentless(adjective, mean, strong, hard, severe)
11
rigorous(adjective, strong, hard, severe, rough)
11
staunch(adjective, calm, clear, strong, sound)
10
unrelenting(adjective, mean, strong, hard, severe)
9
intractable(adjective, hard, rough, difficult)
9
stringent(adjective, hard, severe, difficult)
8
austere(adjective, strong, hard, severe, sharp)
8
hard-line(adjective, characteristic, strong, hard, rough)
8
persistent(adjective, unreasonable, grim, resolute)
8
resistant(adjective, strong, hard, fit)
8
spunky(adjective, strong, lively, determined)
8
stable(adjective, strong, sound, heavy)
8
unsparing(adjective, strong, hard, severe, rough)
7
dense(adjective, person, set, body, strong)
7
inexorable(adjective, mean, strong, hard)
7
set(verb, adjective, calm, strong, hard)
7
unwavering(adjective, calm, strong, secure)
6
authoritarian(noun, adjective, strong, hard, severe)
10 years ago|60k views|share |citing 
APASmart Define. (2016). tough thesaurus. Retrieved September 29, 2026, from https://smartdefine.org/tough/thesaurus/synonyms
ChicagoSmart Define. 2016. "tough thesaurus" https://smartdefine.org/tough/thesaurus/synonyms (accessed September 29, 2026).
HarvardSmart Define 2016, tough thesaurus, Smart Define, viewed 29 September, 2026, <https://smartdefine.org/tough/thesaurus/synonyms>.
MLASmart Define. "tough thesaurus" 30 March 2016. Web. 29 September 2026. <https://smartdefine.org/tough/thesaurus/synonyms>