Temper! Losing head a lot (5)
I believe the answer is:
often
'a lot' is the definition.
(I've seen this in another clue)
'temper losing head' is the wordplay.
'temper' becomes 'soften' (I've seen this before).
'losing head' means to remove the first letter.
'soften' with its initial letter taken off is 'OFTEN'.
(Other definitions for often that I've seen before include "Multiply" , "Turn away" , "More than occasionally" , "Perhaps daily" , "Frequent" .)