Appropriate to invest in trim computer (6)
I believe the answer is:
laptop
'computer' is the definition.
(laptop is a part of computer)
'appropriate to invest in trim' is the wordplay.
'appropriate' becomes 'apt' (synonyms).
'to invest in' is an insertion indicator.
'trim' becomes 'lop' (synonyms).
'apt' put inside 'lop' is 'LAPTOP'.
(Other definitions for laptop that I've seen before include "Kind of computer" , "Aid for businessman" , "Type of computer" , "Some work on this" , "Portable computer" .)