The Collaborative International Dictionary
Seasonal dimorphism
Seasonal \Sea"son*al\, a.
Of or pertaining to the seasons.
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Occurring or being used in a specific season; as, seasonal items for sale.
Seasonal dimorphism (Zo["o]l.), the condition of having two distinct varieties which appear at different seasons, as certain species of butterflies in which the spring brood differs from the summer or autumnal brood.