Pressure wore out authority (5)
I believe the answer is:
'authority' is the definition.
(I've seen this before)
'pressure wore out' is the wordplay.
'pressure' becomes 'p' (scientific abbreviation).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'wore' anagrammed gives 'ower'.
(Other definitions for power that I've seen before include "Ability (to do something)" , "Strength or authority" , "Force, controlling influence 95)" , "Political authority" , "Exponent" .)