sea·son·al /ˈsiznəl, ˈsizṇəl/
  (a.)季節的,依照季節的,週期性的
  seasonal
  季節性的
  seasonal
  季節性
  Sea·son·al a.
  1. Of or pertaining to the seasons.
  2. Occurring or being used in a specific season; as, seasonal items for sale.
  Seasonal dimorphism Zool., 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.
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  seasonal
       adj : occurring at or dependent on a particular season; "seasonal
             labor"; "a seasonal rise in unemployment" [ant: year-round]