Temper -- losing head regularly! (5)
I believe the answer is:
often
'regularly' is the definition.
(often means regularly or frequently)
'temper losing head' is the wordplay.
'temper' becomes 'soften' (I've seen this in another clue).
'losing head' means to remove the first letter.
'soften' with its initial letter removed is 'OFTEN'.
(Other definitions for often that I've seen before include "on many occasions" , "Turn away" , "Quite frequently" , "Multiply" , "Commonly" .)