[ see-zuh-nal-i-tee ]
/ ˌsi zəˈnæl ɪ ti /

noun, plural sea·son·al·i·ties.

the state or quality of being seasonal or dependent on the seasons: the seasonality of Halloween costumes.
Usually seasonalities. a pattern, variation, or fluctuation that is correlated with a season, day of the week, or other period of time: a study of birth seasonalities; You get higher returns in January because of seasonalities in stock prices. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for seasonality