そらみつ

• 虚空見, 虚見津

First attested in the Kojiki (712 CE).

Original derivation likely unknown.^[1][2] Theories include:

• The Nihon Shoki (720 CE) derives this pillow word from 空 (so₁ra, “empty space → sky”) +‎ 見 (mi₁, the 連用形 (ren'yōkei, “stem or continuative form”) of verb 見る (mi₁ru), “to see”) +‎ つ (tu, possessive particle or perfective verbal suffix).
• Mi₁tu is most likely 満つ (mi₁tu), basis of modern 満たす (mitasu, “to fill”, transitive) and 満ちる (michiru, “to be full”, intransitive). By this derivation, "sky-filling or -spreading", rather than "sky-seen", is a more likely interpretation for this pillow word.
• According to Vovin (2011), mi₁tu is borrowed from a Koreanic cognate of Middle Korean 밑 (mith, “under”), in analogy with the Classical Chinese 天下 (tiānxià), meaning “under heaven”.^[3]
• Mi₁tu is likely a pun on 御津 (mi₁-tu, “harbor, port”, honorific), referring to the port in Naniwa, present-day Osaka, where it was the main hub for government ships. (Can this⁽⁺⁾ etymology be sourced?)

そらみつ (so₁ra mi₁tu)

1. a pillow word of uncertain meaning, allusion to 大和 (Yamato₂, a placename, especially “Yamato Province”)

• 空に満つ (so₁ra ni mi₁tu)