蕎麦

Not attested until the middle of the Muromachi period (1336–1573),^[1] as a shortening of older 蕎麦 (soba mugi, literally “soba grain”).^[1][2][3]

Two theories exist regarding the ultimate derivation of the soba element:

• Samuel Martin reconstructs soba as Proto-Japonic *sonpa and derives it as a compound of *so (unknown) +‎ *pa (“feather”). The *pa changes to *ⁿba as an instance of rendaku (連濁).^[4]

• From 稜 (soba, “an edge, a corner”),^[1][3][5][6] in reference to the seed of the plant being a triangular oval shape with protruding corners.^[7]

Considering the late appearance of soba in isolation with the meaning of buckwheat, and the attested earlier senses of side; corner, edge, Martin's reconstruction seems unlikely.

The kanji spelling is an example of jukujikun (熟字訓), from 蕎 (“buckwheat”) +‎ 麦 (“wheat”).

• (Tokyo) そば [sóꜜbà] (Atamadaka – [1])^[5][3][8]
• IPA^(key): [so̞ba̠]

蕎麦(そば) • (soba) 

1. [from the 1400s] buckwheat
2. [from the early 1500s] soba, soba noodle, a variety of Japanese noodle made from buckwheat

   Synonym: 蕎麦切り (sobakiri)

   私(わたし)はあなたに蕎麦(そば)を食(た)べさせたいと思(おも)っています。

   Watashi wa anata ni soba o tabesasetai to omotteimasu.

   I'm thinking about letting you try some soba noodles.

3. [from 1500s or 1600s] a kind of low, flat, broad tea bowl, originally produced on the Korean peninsula and favored in tea ceremony, so called for the color of the glaze
4. [from 1811] (archaic) a night-time streetwalker (specifically an unlicensed prostitute); from the way that night-time sellers of soba noodles via food carts would walk the streets in search of customers
5. [from 1867] (archaic) sixteen of something (when counting); from the way that a length of 16 文 (mon, a traditional Japanese unit of length; 1 mon = approximately 2.4cm) worth of soba noodles would fill a single serving bowl

From Old Japanese. First attested as the ideographic spelling 蕎麦 in a section of the Shoku Nihongi dated to 722.^[1] Later attested in the 本草和名 (Honzō Wamyō, “Main Plants Japanese Names”, a Japanese reference of plants used in Chinese medicine, compiled in 918)^[1][5] with the phonetic spelling 曾波牟岐 (so pa mu gi).^[1]

Analyzable as a compound of 蕎 (soba, “buckwheat”) +‎ 麦 (mugi, “dry-field grain”).^[1][9] However, the soba portion is not attested in isolation to mean "buckwheat" until the middle of the Muromachi period (1336–1573).^[1] It appears that soba was originally the word 稜 (soba, “corner, angle”) in reference to the angular shape of the buckwheat grain.^[1][5][3] Compare the similar derivation of English buckwheat, where the buck element is cognate with beech and refers to the angular shape of the beechnut. An old Japanese name for the beech tree is in fact 柧棱木 (soba no ki), again in reference to the angular shape of the beechnut.

• IPA^(key): [so̞ba̠mɯ̟ɡʲi]

蕎(そば)麦(むぎ) • (sobamugi) 

1. [722–???] (archaic) buckwheat

/sobamuɡi/ → /somamuɡi/

Shift in pronunciation from sobamugi. First attested in the early 1100s.^[1]

• IPA^(key): [so̞ma̠mɯ̟ɡʲi]

蕎(そま)麦(むぎ) • (somamugi) 

1. [1100s–???] (archaic) buckwheat

Possibly a borrowing from Middle Chinese 蕎麥 (MC kjew|gjew meak). First attested in a section of the Shoku Nihongi dated to 722,^[1] and additionally later in imported works written in Chinese by Bai Juyi (772–846).^[1]

Unclear if this reading was ever prevalent; use might have been limited to kanbun contexts. Not listed in many Japanese dictionaries.^[5][3][9]

• IPA^(key): [kʲo̞ːba̠kɯ̟]

蕎(きょう)麦(ばく) • (kyōbaku) 

1. [722–???] (obsolete) buckwheat