Frequently melt missing shillings (5)
I believe the answer is:
often
'frequently' is the definition.
('often' can be a synonym of 'frequently')
'melt missing shillings' is the wordplay.
'melt' becomes 'soften'.
'missing' suggests deleting specific letters.
'shillings' becomes 's'.
'soften' with 's' taken out is 'OFTEN'.
(Other definitions for often that I've seen before include "Regularly" , "Much of the time" , "In many instances" , "Frequently, many times" , "A lot" .)