What's the "een" in Halloween?
1899, from Japanese, where it is singular of haikai, in haikai no renga "jesting linked-verse;" originally a succession of haiku linked together into one poem. The form developed mid-16c. "Traditionally, there is mention of a season of the year somewhere in a haiku, as a means of establishing the poem's tone, though this may be only the slightest suggestion." [Miller Williams, "Patterns of Poetry," Baton Rouge: Louisiana State University, 1986].
A form of Japanese poetry. A haiku expresses a single feeling or impression and contains three unrhymed lines of five, seven, and five syllables, respectively.