Cold space, we’re told (5)
I believe the answer is:
rheum
'cold' is the definition.
(I've seen this in another clue)
'space we're told' is the wordplay.
'space' becomes 'room' (enough space or room to do something).
'we're told' indicates a 'sounds like' (homophone) clue.
'room' sounds like 'RHEUM'.
(Other definitions for rheum that I've seen before include "Watery discharge from eyes or nose" , "Flowing water" , "Watery fluid" , "nasal discharge" , "Watery mucous discharge" .)