Work out tax without sign of hesitation (8)
I believe the answer is:
exercise
'work out' is the definition.
(I know that work out can be written as exercise)
'tax without sign of hesitation' is the wordplay.
'tax' becomes 'excise' (excise is a kind of tax).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'sign of hesitation' becomes 'er'.
'excise' enclosing 'er' is 'EXERCISE'.
(Other definitions for exercise that I've seen before include "Gym activity?" , "Practice task" , "problem" , "Task set to practise" , "Train, work out" .)