Trim graduate climbing hill-range (7)
I believe the answer is:
abridge
'trim' is the definition.
(thesaurus)
'graduate climbing hill-range' is the wordplay.
'graduate' becomes 'ba'.
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'hill-range' becomes 'ridge' (I've seen this before).
'ba' reversed gives 'ab'.
'ab'+'ridge'='ABRIDGE'
(Other definitions for abridge that I've seen before include "Reduce the length of" , "Abbreviate, contract" , "Shorten, a book say, without losing the sense" , "Remove sections" , "Curtail" .)