14
biennial
9
constant
9
biannual
8
perennial
8
semiannual
7
two-year
4
perpetual
3
static
3
stationary
3
unalterable
3
aperiodic
2
eternal
2
lasting
2
permanent
2
strong
2
continual
2
decennial
2
staunch
2
steadfast
2
steady
<12>
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APASmart Define. (2015). annual thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/annual/thesaurus/antonyms
ChicagoSmart Define. 2015. "annual thesaurus" https://smartdefine.org/annual/thesaurus/antonyms (accessed September 24, 2026).
HarvardSmart Define 2015, annual thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/annual/thesaurus/antonyms>.
MLASmart Define. "annual thesaurus" 10 April 2015. Web. 24 September 2026. <https://smartdefine.org/annual/thesaurus/antonyms>