Number out there? (5)
I believe the answer is:
ether
'number' is the definition.
(I've seen this before)
'out there?' is the wordplay.
'out' indicates an anagram.
'there' is an anagram of 'ETHER'.
(Other definitions for ether that I've seen before include "It could knock you out" , "Colourless, highly flammable liquid" , "Chemical solvent" , "Liquid used as anaesthetic/ solvent" , "Anaesthetic is, strangely, there" .)