Related Clues:

• The blue number the girl's put on out of this world!
• Old-time knockout gas
• Volatile organic liquid once used as a general anaesthetic
• The upper air
• There (anag.)
• Clear upper air
• Solvent used by Rosie the Riveter
• Number three, possibly
• Anaesthetic required in gene therapy
• A theatrical number?
• About to spin having absorbed the anaesthetic?
• Theatrical number
• Three (anag.)
• Number three, perhaps
• Once widely-used anaesthetic