Ether

An Ether is an item that restores 3 MP or magic points in Kingdom Hearts. However, in Kingdom Hearts II it fully restores MP (if there is some left in the bar) or it can be used to reduce the MP Charge Gauge.

In Kingdom Hearts 358/2 Days, it's in form of an item panel which restores one cast of each magic you've installed.

Etymology
Ether is a class of organic compounds that contain an ether group.

Ether