俳句 and 短歌: a seasonal haiku and a tanka about the sea
Follow a 俳句 composed with a seasonal word and a 短歌 about the sea, distinguishing 一首 as one poem from the morae of Japanese meter.
俳句: composing with a seasonal word and appearing in print
「季節の言葉を入れて短い俳句を作った。」 means “I composed a short haiku using a seasonal word.” 俳句（はいく） means haiku. This poem was composed using a seasonal word; that description of one composition is not an exceptionless rule for every haiku.
「祖母の俳句が町の広報紙に載った。」 means “My grandmother's haiku appeared in the town newsletter.” 町の広報紙に載った describes the grandmother’s haiku appearing in the town newsletter. Composing a poem in the first example and having one appear in print in this example are different events.
短歌: composing one poem and appreciating an old poem
「旅で見た海を題に短歌を一首詠んだ。」 means “I composed a Japanese thirty-one-syllable poem about the sea I saw on my trip.” 旅で見た海を題に makes the sea seen on the trip the poem’s subject. 一首 counts one tanka, and 詠んだ describes composing that one poem.
「授業で古い短歌の表現を味わった。」 means “In class, we appreciated the language of an old Japanese poem.” 味わった describes appreciating the language of an old poem in class. The person appreciating that language is not thereby identified as the poem’s original author.
The definition and the unit of poetic counting
The definition of 短歌（たんか） is “Japanese thirty-one-syllable poem”. In Japanese poetic meter, the thirty-one 音 are counted as morae, or timing units. Morae and syllables are different units, so the gloss should not be read as thirty-one ordinary syllables in every language.
一首 counts a whole poem, while 31音 counts units of meter. Connect composing a poem about the sea, having a haiku appear in a newsletter, and appreciating an old poem’s language with the separate objects and actions in their sentences.
What does 一首 count in 短歌を一首詠んだ?
Show the answer and why
It counts one tanka, a whole poem. This count is distinct from the 31音 of the meter. Composing a poem about the sea and appreciating an old poem’s language in class are also separate actions.