Where does “東琴” come from?

東琴 (Japanese) comes from Japanese 東, from Old Japanese 東, from Old Japanese 天, from Proto-Japonic *amay.

東琴 (Japanese): a six-stringed koto or zither used to perform...

Definitions

東琴 traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Japanese	東	the east; the Orient; an easterly
2	Old Japanese	東	the east; the lands east of the 都
3	Old Japanese	天	sky, heavens
4	Proto-Japonic	*amay	—

Step	Language	Word	Meaning
1	Japanese	琴	koto: a Japanese zither derived from the Chinese...
2	Middle Chinese	琴	—