51 entries under stiff topic. ×

23
tough(adjective, strong, firm, solid)
20
adamantine(adjective, strong, tough, severe, firm)
18
flinty(adjective, strong, hard, firm, solid)
18
impenetrable(adjective, firm, solid, rigid)
9
unyielding(adjective, strong, hard, tough, severe)
8
rigid(adjective, strong, hard, severe, firm)
6
firm(adjective, strong, hard, tough, severe)
5
solid(adjective, strong, hard, tough, severe)
5
hard(adjective, strong, severe, firm, harsh)
5
resistant(adjective, strong, hard, tough, solid)
5
rocky(adjective, firm, rigid, unyielding)
5
tight(adjective, strong, hard, tough, solid)
4
durable(adjective, strong, hard, tough, firm)
4
stony(adjective, firm, rigid, unyielding)
3
strong(adjective, hard, firm, solid)
2
harsh(adjective, severe, firm, solid)
1
definite(adjective, severe, firm, harsh, solid)
1
inflexible(adjective, strong, hard, severe, firm)
1
resilient(adjective, strong, hard, solid)
1
set(adjective, severe, firm, harsh, solid)
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APASmart Define. (2016). unbreakable thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/unbreakable/thesaurus/synonyms
ChicagoSmart Define. 2016. "unbreakable thesaurus" https://smartdefine.org/unbreakable/thesaurus/synonyms (accessed September 24, 2026).
HarvardSmart Define 2016, unbreakable thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/unbreakable/thesaurus/synonyms>.
MLASmart Define. "unbreakable thesaurus" 5 January 2016. Web. 24 September 2026. <https://smartdefine.org/unbreakable/thesaurus/synonyms>