2
imperative(adjective, essential, prime, main, necessary)
1
consequential(adjective, important, essential, main, chief)
1
constitutive(adjective, important, significant, substantial, essential)
1
critical(adjective, main, principal, predominant)
1
elementary(adjective, original, primary, initial, pristine)
1
inherent(adjective, base, basic, key, main)
1
intrinsic(adjective, base, basic, key, main)
1
momentous(adjective, important, essential, main, chief)
1
pivotal(adjective, base, basic, key, main)
1
preeminent(adjective, important, essential, main, chief)
1
primordial(adjective, base, basic, key, main)
1
substantial(adjective, base, basic, key, main)
1
uppermost(adjective, important, essential, main, chief)
1
weighty(adjective, important, essential, main, chief)
1
arch(adjective, important, essential, main, chief)
1
champion(adjective, important, essential, main, chief)
1
effective(adjective, important, essential, main, chief)
1
especial(adjective, important, essential, main, chief)
1
grand(adjective, important, essential, main, chief)
1
highest(adjective, important, essential, main, chief)
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APASmart Define. (2015). ancillary thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/ancillary/thesaurus/antonyms
ChicagoSmart Define. 2015. "ancillary thesaurus" https://smartdefine.org/ancillary/thesaurus/antonyms (accessed September 23, 2026).
HarvardSmart Define 2015, ancillary thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/ancillary/thesaurus/antonyms>.
MLASmart Define. "ancillary thesaurus" 10 April 2015. Web. 23 September 2026. <https://smartdefine.org/ancillary/thesaurus/antonyms>