A lot of effort to get a new advertising feature (6)
I believe the answer is:
slogan
'advertising feature' is the definition.
(an advert might feature a slogan)
'a lot of effort to get a new' is the wordplay.
'a lot of effort' becomes 'slog' (a slog is a difficult task or process).
'to get' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'slog'+'a'+'n'='SLOGAN'
(Other definitions for slogan that I've seen before include "Identifying catchword" , "Advertising catchphrase" , "Short catchy phrase used in advertising" , "advertising catch phrase" , "Ad. catchphrase" .)