Climbing part of Munro, dalesman, trim (5)
I believe the answer is:
adorn
'trim' is the definition.
(I've seen this in another clue)
'climbing part of munro dalesman' is the wordplay.
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'part of' indicates a hidden word.
'nroda' is hidden in the letters of 'munro dalesman'.
'nroda' in reverse letter order is 'ADORN'.
(Other definitions for adorn that I've seen before include "dress" , "Improve appearance" , "Deck" , "Beautify - decorate - enhance" , "Festoon" .)