Hard work, introducing a new catchphrase (6)
I believe the answer is:
slogan
'catchphrase' is the definition.
(eg a political catchphrase)
'hard work introducing a new' is the wordplay.
'hard work' becomes 'slog' (a slog is a long or difficult task).
'introducing' means one lot of letters go next to another (some letters go before others).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'slog'+'a'+'n'='SLOGAN'
(Other definitions for slogan that I've seen before include "Battle cry - advertising phrase" , "Marketing phrase" , "Memorable advertising phrase" , "Shibboleth" , "Short catchy phrase used in advertising" .)