Bitcoin alternative, familiarly (5)

I believe the answer is:

ether

(Other definitions for ether that I've seen before include "Anaesthetic; clear sky (poetic)" , "Anaesthetic is, strangely, there" , "Highly flammable liquid once used as an anaesthetic" , "Volatile solvent" , "Solvent; clear sky (poet.)" .)

I've seen this clue in the LA Times.

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