寝巻き

First attested in a text from 1548.[1]

The term is a compound, although the exact derivation is slightly unclear.

• May be a compound of 寝間 (nema, “bedroom”, literally “sleeping + space”) +‎ 着 (ki, “wear, wearing”, the 連用形 (ren'yōkei, “continuative or stem form”) of verb 着る (kiru, “to wear”), referring more specifically to the upper body).

However, the term 寝間 (nema) is not attested until 1686, and the 寝間着 spelling may be later ateji rather than indicative of derivation.

• May be a compound of 寝 (ne, “sleep, sleeping”) +‎ 巻き (maki, “roll, rolling; winding”).[2]

However, the semantics are slightly strange, as sleeping garments are not rolled. The latter portion may instead be in reference to the way that robes are wound or wrapped around the body.

• (Tokyo) ねまき [nèmákí] (Heiban – [0])[2][3][4]
• IPA^(key): [ne̞ma̠kʲi]

寝(ね)巻(ま)き • (nemaki) 

1. [from 1548] nightwear, nightgown, pajamas

   Synonyms: 寝衣 (shin'i), パジャマ (pajama), ナイトガウン (naitogaun)

• 浴衣(ゆかた) (yukata): a thin, light kimono, worn for sleeping or for summer.