Thrice married orderly (4)
I believe the answer is:
'orderly' is the definition.
'thrice married' is the wordplay.
'thrice' becomes 'tri' (I am not sure about this - if you are sure you should believe this answer much more).
'married' becomes 'm'.
Can you help me to learn more?
(Other definitions for trim that I've seen before include "Neat and tidy as a town in Meath" , "Cut off; slim and fit" , "Reduce slightly" , "Svelte" , "Prune or pare" .)