He handed Will a small leather flask.
“Drink this,” he said. “It is called everenth. It will restore
some of your strength and help you resist, if Lotan appears to
you again.”
Will took a tentative sip. The drink tasted slightly bitter,
like unsweetened tea, but almost immediately he felt a warmth
flowing into him.

--from The Shadow of Malabron, Chapter XVII, page 217

The drink that Moth gives Will is called everenth. It is a herbal drink brewed of extracts from several plants collected by the Shee n'ashoon, but especially from the hard black berries of the evergreen shrub called everenth, for which then drink is named. Everenth grows only in the windy highlands of Lyrr, far to the northwest of the Bourne.

As Moth says, one of everenth's qualities is to restore strength, although this is somewhat misleading. In our world we drink coffee or tea because we think it gives us energy, when in fact the energy is already there inside us, in potential -- the drink merely allows our bodies to access it. More than anything else, everenth is a drink that clears the heart and mind, allowing you to find that energy within, that you thought was lost but was always there.