Trendy pants Catherine's gift from Will (11)
I believe the answer is:
inheritance
'gift from will' is the definition.
'inheritance' can be an answer for 'will' (thesaurus). I am not sure about the 'gift from' bit.
'trendy pants catherine's' is the wordplay.
'trendy' becomes 'in' ('in' can mean fashionable).
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'catherine' is an anagram of 'heritance'.
'in'+'heritance'='INHERITANCE'
Can you help me to learn more?
(Other definitions for inheritance that I've seen before include "Things handed down" , "Ancient heir (anag.)" , "Something handed down" , "Legacy" , "What one may come into" .)