Fierce diatribe about current measure (7)
I believe the answer is:
rampant
'fierce' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I don't see?
'diatribe about current measure' is the wordplay.
'diatribe' becomes 'rant' (I've seen this in other clues).
'about' is an insertion indicator.
'current measure' becomes 'amp' (short for ampere, unit of electrical current).
'rant' placed around 'amp' is 'RAMPANT'.
Can you help me to learn more?
(Other definitions for rampant that I've seen before include "Uncontrolled" , "Unrestrained and violent" , "running wild" , "Out of control" , "Growing or spreading uncontrollably" .)