A haiku traditionally contains a kigo, a defined word or phrase that symbolizes or implies the season of the poem, which is drawn from a saijiki, an extensive but defined list of such words.
Kigo are often in the form of metonyms and can be difficult for those who lack Japanese cultural references to spot. The BashÅ examples below include "kawazu", "frog" implying spring, and "shigure", a rain shower in late autumn or early winter. Kigo are not always included in non-Japanese haiku or by modern writers of Japanese "free-form" haiku.
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