Tax it out of frivolity (4)
I believe the answer is:
levy
'tax' is the definition.
(I know that tax is a more specific form of the action levy)
'it out of frivolity' is the wordplay.
'out of' suggests deleting specific letters ('out of' can mean no longer having).
'frivolity' becomes 'levity' (levity is a kind of frivolity).
'levity' with 'it' taken out is 'LEVY'.
(Other definitions for levy that I've seen before include "Sum of money raised" , "Money raised from taxes, etc" , "Impose and collect (money)" , "Toll" , "An imposed tax or duty" .)