Use tax cut by Queen (8)
I believe the answer is:
exercise
'use' is the definition.
(exercising is a kind of using)
'tax cut by queen' is the wordplay.
'tax' becomes 'excise' (excise is a kind of tax).
'cut by' indicates putting letters inside.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'excise' enclosing 'er' is 'EXERCISE'.
(Other definitions for exercise that I've seen before include "Task performed to develop skill" , "Gym activity?" , "Physical exertion for keeping fit" , "Task for pupil" , "that every prisoner should have" .)