Hard work plus a new catchphrase (6)
I believe the answer is:
slogan
'catchphrase' is the definition.
(I've seen this before)
'hard work plus a new' is the wordplay.
'hard work' becomes 'slog' (I've seen this before**).
'plus' says to put letters next to each other.
'a new' becomes 'an' (I've seen this in other clues).
'slog'+'an'='SLOGAN'
(Other definitions for slogan that I've seen before include "Marketing phrase" , "Battle cry - advertising phrase" , "advertising catch phrase" , "Rallying cry" , "'Motto, watchword (6)'" .)