17 entries under harden topic. ×

1
toughen(verb, strengthen)
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acclimate(verb, strengthen)
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acclimatize(verb, strengthen)
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anneal(verb, strengthen)
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beef up(expression, strengthen)
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brutalize(verb, strengthen)
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build up(expression, strengthen)
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climatize(verb, strengthen)
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develop(verb, strengthen)
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firm up(expression, strengthen)
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fortify
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inure(verb, strengthen)
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reinforce
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season(verb, strengthen)
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shore up(expression, strengthen)
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strengthen
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temper(verb, strengthen)
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APASmart Define. (2013). make difficult thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/make_difficult/thesaurus/synonyms
ChicagoSmart Define. 2013. "make difficult thesaurus" https://smartdefine.org/make_difficult/thesaurus/synonyms (accessed September 21, 2026).
HarvardSmart Define 2013, make difficult thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/make_difficult/thesaurus/synonyms>.
MLASmart Define. "make difficult thesaurus" 18 May 2013. Web. 21 September 2026. <https://smartdefine.org/make_difficult/thesaurus/synonyms>