4
significant(adjective, important, essential, prime, main)
3
foremost(adjective, adverb, important, master, essential)
3
basal(adjective, base, basic, key, main)
3
dominant(adjective, essential, prime, vital, necessary)
3
elemental(adjective, base, basic, key, main)
3
first(adjective, important, master, essential, key)
3
head(noun, adjective, important, essential, main)
3
indispensable(adjective, base, basic, key, main)
3
paramount(adjective, important, essential, main, chief)
3
primal(adjective, base, important, essential, basic)
3
supreme(adjective, important, essential, main, chief)
3
considerable(adjective, essential, prime, vital, necessary)
3
constitutional(adjective, essential, prime, vital, necessary)
3
controlling(adjective, important, essential, main, chief)
3
outstanding(adjective, important, essential, main, chief)
3
stellar(adjective, important, essential, main, chief)
2
basic(adjective, essential, prime, main, necessary)
2
fundamental(adjective, essential, prime, main, necessary)
2
initial(adjective, essential, prime, vital, necessary)
2
decisive(adjective, essential, prime, main, necessary)
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APASmart Define. (2015). ancillary thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/ancillary/thesaurus/antonyms
ChicagoSmart Define. 2015. "ancillary thesaurus" https://smartdefine.org/ancillary/thesaurus/antonyms (accessed September 22, 2026).
HarvardSmart Define 2015, ancillary thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/ancillary/thesaurus/antonyms>.
MLASmart Define. "ancillary thesaurus" 10 April 2015. Web. 22 September 2026. <https://smartdefine.org/ancillary/thesaurus/antonyms>