Dog with dog lead evenly trimmed (9)
I believe the answer is:
curtailed
'trimmed' is the definition.
(thesaurus)
'dog with dog lead evenly' is the wordplay.
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'with' means one lot of letters go next to another.
'dog' becomes 'tail' (synonyms).
'evenly' means one should take alternating letters (the letters in even-numbered positions).
The alternate letters of 'lead' are 'ed'.
'cur'+'tail'+'ed'='CURTAILED'
(Other definitions for curtailed that I've seen before include "Clipped" , "Reduced" , "Broken off" , "docked" , "Made short" .)