Breathing space regarding nastiness (7)
I believe the answer is:
respite
'breathing space' is the definition.
(I've seen this in another clue)
'regarding nastiness' is the wordplay.
'regarding' becomes 're' ('re' means regarding or about).
'nastiness' becomes 'spite' (synonyms).
're'+'spite'='RESPITE'
(Other definitions for respite that I've seen before include "Short let-up" , "Pause from exertion, etc" , "Pause to rest" , "Abatement, rest" , "Short period of relief" .)