noun
first line of a poem; opening phrase
Specifically refers to the first five syllables in a tanka, or more broadly the first line of any poem. A technical term in Japanese poetry.
短歌の初句は五音で始まる。
The first line of a tanka begins with five syllables.
この俳句の初句が特に印象的だ。
The opening phrase of this haiku is especially striking.