Where does “六衛府” come from?

六衛府 (Japanese) comes from Japanese 衛府, from Japanese 衛, from Middle Chinese えい, from Middle Chinese 映.

六衛府 (Japanese): the Six Guards since the early Heian period (左近衛府, 右近衛府, 左衛門府, 右衛門府, 左兵衛府 and 右兵衛府)

Definitions

the Six Guards since the early Heian period (左近衛府, 右近衛府, 左衛門府, 右衛門府, 左兵衛府 and 右兵衛府)

六衛府 traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Japanese	衛府	a 律令 imperial guard squad
2	Japanese	衛	defense; to guard
3	Middle Chinese	えい	—
4	Middle Chinese	映	—

Step	Language	Word	Meaning
1	Japanese	六	six; a name of a hole of a wind instrument
2	Late Middle Chinese	六	—