Always some reversal (4)
I believe the answer is:
ever
'always' is the definition.
(synonyms)
'some reversal' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'EVER' is hidden in the letters of 'reversal'.
(Other definitions for ever that I've seen before include "Perpetually" , "Possibly" , "Continuously" , "Always and permanent" , "On any occasion" .)