7
momentous(adjective, importance, valuable, main, notable)
7
outstanding(adjective, importance, valuable, main, notable)
7
portentous(adjective, importance, valuable, main, notable)
7
purposeful(adjective, importance, valuable, main, notable)
7
remarkable(adjective, importance, valuable, main, notable)
7
responsible(adjective, importance, valuable, main, notable)
7
significative(adjective, importance, valuable, main, notable)
7
solemn(adjective, importance, valuable, main, notable)
7
substantial(adjective, importance, valuable, main, notable)
7
vital(adjective, importance, valuable, main, notable)
6
confronting(verb, opposing, confronting, defying)
6
counteracting(verb, adjective, opposing, oppositional, defying)
6
demanding(adjective, hard, tough, severe, difficult)
6
objecting(verb, adjective, opposing, disagreeing, oppositional)
6
protesting(verb, adjective, opposing, oppositional)
6
provoking(verb, adjective, stimulating)
6
questioning(verb, adjective, questioning)
5
arduous(adjective, hard, great, tough, severe)
5
resisting(verb, adjective, opposing, oppositional, defying)
5
rousing
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APASmart Define. (2016). challenging thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/challenging/thesaurus/synonyms
ChicagoSmart Define. 2016. "challenging thesaurus" https://smartdefine.org/challenging/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2016, challenging thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/challenging/thesaurus/synonyms>.
MLASmart Define. "challenging thesaurus" 2 March 2016. Web. 22 September 2026. <https://smartdefine.org/challenging/thesaurus/synonyms>