梅雨 - Wiktionary, the free dictionary

Refers to the season when fruits of Prunus mume ripen.

梅雨

1. Meiyu (the East Asian rainy season)

   • 洛下麥秋月，江南梅雨天。 [Classical Chinese, trad.]
     洛下麦秋月，江南梅雨天。 [Classical Chinese, simp.]

     From: Bai Juyi (白居易), c. 9th century. 《和夢得夏至憶蘇州呈盧賓客》

     Luòxià màiqiū yuè, jiāngnán méiyǔ tiān. [Pinyin]

     The early-summer moon lights Luoyang's fields, when Jiangnan is overcast with plum-rain.

   • 梅雨，溪流漲盛，先生扶病往觀。 [Classical Chinese, trad.]
     梅雨，溪流涨盛，先生扶病往观。 [Classical Chinese, simp.]

     From: Various editors. c. 13th century. A Collection of Conversations of Master Zhu (《朱子語類》)

     Méiyǔ, xīliú zhǎng shèng, xiānshēng fúbìng wǎng guān. [Pinyin]

     It was the summer rainy season; streams were overflowing. Master Zhu, despite illness, went out to watch the flood.

2. rain that falls during the Meiyu season; summer rain

• (Hokkien) 黃酸雨／黄酸雨
• (Wu) 黃梅雨／黄梅雨

• 夏糜

First attested in the mid-Muromachi period.^[1]

Derivation unclear, likely theories include:

• May be cognate with 露 (tsuyu, “dew, dewdrop”), from the way the rainy season causes everything to be covered in drops that may look like dew. However, the pitch accent differs, as 露 (tsuyu) has either an 頭高型 (atamadaka-gata) or 尾高型 (odaka-gata) pattern, while 梅雨 (tsuyu) has a 平板型 (heiban-gata) pattern.
• Alternatively, may be cognate with classical verb 熟ゆ (tsuyu, modern 熟える (tsueru), “to become ripe”), as plums ripen during the rainy season. In light of the pitch accent and semantics, this derivation appears more likely.

Orthographic borrowing from Chinese 梅雨 (méiyǔ).

• (Tokyo) つゆ [tsùyú] (Heiban – [0])^[2][3]
• IPA^(key): [t͡sɨjɯ̟]

梅雨(つゆ) • (tsuyu) 

1. the East Asian rainy season (from early June to early/mid-July)

   Synonym: 五月雨 (samidare)

• 梅雨(つゆ)の中休(なかやす)み (tsuyu no nakayasumi)
• 梅雨(つゆ)の走(はし)り (tsuyu no hashiri), 走(はし)り梅雨(づゆ) (hashirizuyu)

From Middle Chinese compound 梅雨 (MC mwoj hjuX), in poetic reference to the season when plums grow or ripen.^[1][3]

Alternatively, the 黴雨 spelling may have been the original spelling. This is homophonous in Middle Chinese, and literally means “mold + rain”, in reference to how moldy things get during this season of constant humidity.^[1][3][4]

• (Tokyo) ばいう [báꜜìù] (Atamadaka – [1])^[2][3]
• IPA^(key): [ba̠iɯ̟]

梅(ばい)雨(う) • (baiu) 

1. the East Asian rainy season (from early June to early/mid-July)

   Synonym: 五月雨 (samidare)

• 梅(ばい)雨(う)前線(ぜんせん) (baiu zensen)
• 梅(ばい)雨(う)末(まっ)期(き)豪(ごう)雨(う) (baiu makki gōu)

梅雨 • (mae'u) (hangeul 매우)

1. hanja form^? of 매우 (“East Asian rainy season”)