Where does “東シナ海” come from?

東シナ海 (Japanese) comes from Japanese 東, from Old Japanese 東, from Old Japanese 天, from Proto-Japonic *amay.

東シナ海 (Japanese): the East China Sea

Definitions

the East China Sea

Ancestry of “東シナ海”, step by step

東シナ海 traces back through 3 separate lines of ancestry.

via Japanese 東

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	—

via Japanese シナ

Step	Language	Word	Meaning
1	Japanese	シナ	Seriphidium cinum, syn. Artemisia cina: also known as santonica, Levant wormseed, and wormseed; an herbaceous perennial of the daisy family, historically used as a vermifugic anthelmintic (a drug to rid the body of parasitic worms)
2	Japanese	科	department, section; family; crime; wrongdoing
3	Japanese	品	article, goods; stock; quality
4	Middle Chinese	品	—

via Japanese 海

Step	Language	Word	Meaning
1	Japanese	海	a sea, an ocean; a lake; an object covering over...
2	Old Japanese	うな	—

Every word from Proto-Japonic *amay →Every word from Old Japanese 天 →Every word from Old Japanese 東 →