Temper beginning to show frequently (6)
I believe the answer is:
soften
'temper' is the definition.
(I've seen this before)
'beginning to show frequently' is the wordplay.
'beginning to' suggests taking the first letters.
'frequently' becomes 'often' ('often' can be a synonym of 'frequently').
The first letter of 'show' is 's'.
's'+'often'='SOFTEN'
(Other definitions for soften that I've seen before include "Mollify" , "Make less hard or become less severe" , "Make less firm" , "To moderate" , "Make more plastic" .)