Officer with popular name (5)
I believe the answer is:
colin
'name' is the definition.
'officer with popular' is the wordplay.
'officer' becomes 'col' (short for colonel).
'with' says to put letters next to each other.
'popular' becomes 'in' ('in' can mean trendy).
'col'+'in'='COLIN'
(Other definitions for colin that I've seen before include "Man's name" , "--- Wilson, Eng. writer (The Outsider)" .)