1
exacting
1
flaky
1
flinty
1
fossilised
1
fossilized
1
fragile
1
friable
1
fussy
1
goal-oriented
1
hard-core
1
hardheaded
1
hidebound
1
immovable
1
immutable(adjective, unchangeable)
1
implacable
1
inhumane(adjective, bright)
1
intractable
1
invariable
1
iron(adjective, hard, tough, soft, inflexible)
1
ironclad
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APASmart Define. (2016). flexible thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/flexible/thesaurus/antonyms
ChicagoSmart Define. 2016. "flexible thesaurus" https://smartdefine.org/flexible/thesaurus/antonyms (accessed September 24, 2026).
HarvardSmart Define 2016, flexible thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/flexible/thesaurus/antonyms>.
MLASmart Define. "flexible thesaurus" 28 March 2016. Web. 24 September 2026. <https://smartdefine.org/flexible/thesaurus/antonyms>