Resident worker following popular custom (10)
I believe the answer is:
inhabitant
'resident' is the definition.
(I know that resident can be written as inhabitant)
'worker following popular custom' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'following' means one lot of letters go next to another.
'popular' becomes 'in' ('in' can mean trendy).
'custom' becomes 'habit' (habit is a kind of custom).
'in'+'habit'='inhabit'
'ant' after 'inhabit' is 'INHABITANT'.
(Other definitions for inhabitant that I've seen before include "One who stays in" , "One living in a place" , "Resident" , "One occupying a place" .)