Mean to hold on this evening (7)
I believe the answer is:
tonight
'this evening' is the definition.
('tonight' can be a synonym of 'this evening')
'mean to hold on' is the wordplay.
'mean' becomes 'tight' ('tight' can be a synonym of 'mean'**).
'to hold' indicates putting letters inside.
'tight' placed around 'on' is 'TONIGHT'.
(Other definitions for tonight that I've seen before include ""Not ____, Josephine!"" , "song from West Side Story" , "later in the day" , "Selection from West Side Story" , "West Side Story number" .)