noun
opening verse of a renga
Specifically the first 17-syllable (5-7-5) verse in a linked-verse sequence (renga). This is a technical term from classical poetry.
See also: 揚げ句 (あげく)
連歌では、発句が全体の季節感を決める重要な役割を果たす。
In renga, the opening verse plays an important role in setting the seasonal tone of the whole sequence.
noun
By extension, 発句 can refer to a standalone haiku, especially in older usage. In modern Japanese, 俳句 is the usual word for haiku.
芭蕉の発句には、自然への深い洞察が感じられる。
In Bashō's haiku, one can feel a deep insight into nature.
noun
first five-syllable line of a tanka
Rare technical use; refers to the opening 5-syllable line of a tanka (5-7-5-7-7). This usage is mostly found in classical poetry commentary.
この歌の発句は、読者の注意を引く力強い表現で始まる。
The first line of this tanka begins with a powerful expression that grabs the reader's attention.
短歌 is the 31-syllable poem form; 発句 can refer to its first 5-syllable line in classical contexts, but this usage is rare.
From 発 (starting, opening) + 句 (verse, phrase). The term originated in renga composition, where the first verse was called 発句.