Answer:

ether

Answer	Crossword Clue
ETHER	Medieval atmosphere
ETHER	Old-time anaesthetic
ETHER	Old-time anesthetic

ETHER	Solvent
ETHER	Anesthetic
ETHER	Anesthetic of old
ETHER	Common solvent
ETHER	Erstwhile anesthetic
ETHER	It put people to sleep
ETHER	It's a gas
ETHER	It's a knockout

ETHER	Old anesthetic
ETHER	Region just past the ozone
ETHER	It'll knock you out
ETHER	Blue sky
ETHER	Bygone anesthetic
ETHER	Space, poetically
ETHER	Upper atmosphere
ETHER	Early number?

ETHER	Early anesthetic
ETHER	Compound number?
ETHER	Knockout stuff
ETHER	Wild blue yonder
ETHER	Cyberspace metaphor
ETHER	Former anesthetic
ETHER	Outmoded anesthetic
ETHER	Aristotle's "fifth element"

ETHER	Heavens
ETHER	Old number?
ETHER	One-time surgery aid
ETHER	Upper regions
ETHER	It can knock you out
ETHER	Old hospital supply
ETHER	It can put you out
ETHER	Old knockout cause

ETHER	Early surgery aid
ETHER	Number no longer used?
ETHER	Old knockout agent
ETHER	Out-of-use anesthetic
ETHER	Anesthetic of yore

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.