6
cake(verb, close, set, fix, settle)
6
tighten up(verb, expression, phrasal verb)
5
crystallize(verb, form, close, set, fix)
5
indurate(verb, dull, close, set, fix)
5
ossify(verb, calm, close, set, fix)
5
prop(noun, verb, support, calm, fix)
5
rigidify(verb, place, set, secure, settle)
5
steel(verb, dull, close, set, fix)
5
temper(verb, close, set, fix, settle)
4
consolidate(verb, close, place, set, fix)
4
inspissate(verb, swell, expand, condense, harden)
4
invigorate(verb, encourage, restore, revive, refresh)
4
support(noun, verb, calm, fix, increase)
3
back(verb, keep, maintain, encourage, raise)
3
beef up(verb, expression, phrasal verb, support, increase)
3
benumb(verb, freeze, bite, chill, harden)
3
buttress(verb, support, calm, close, set)
3
cement(verb, close, place, set, fix)
3
energize(verb, support, increase, encourage, restore)
3
gel(verb, form, set, fix, develop)
11 years ago|7.2k views|share |citing 
APASmart Define. (2015). stiffen thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/stiffen/thesaurus/synonyms
ChicagoSmart Define. 2015. "stiffen thesaurus" https://smartdefine.org/stiffen/thesaurus/synonyms (accessed September 24, 2026).
HarvardSmart Define 2015, stiffen thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/stiffen/thesaurus/synonyms>.
MLASmart Define. "stiffen thesaurus" 13 April 2015. Web. 24 September 2026. <https://smartdefine.org/stiffen/thesaurus/synonyms>