Clipped dunce’s head with a spanner first (8)
I believe the answer is:
'clipped' is the definition.
'dunce's head with a spanner first' is the wordplay.
'head' indicates taking the first letters.
'with' says to put letters next to each other.
'spanner' becomes 'bridge' (I've seen this before**).
'first' is a charade indicator (letters next to each other).
The initial letter of 'dunces' is 'd'.
'a' next to 'bridge' is 'abridge'.
'd' put after 'abridge' is 'ABRIDGED'.
(Other definitions for abridged that I've seen before include "Shortened as book may be" , "Shorter" , "Cut short - big adder (anag)" , "Abbreviated, contracted" , "Epitomised" .)