Zip on wife's new frock (4)
I believe the answer is:
gown
'frock' is the definition.
(gown is a kind of frock)
'zip on wife's new' is the wordplay.
'zip' becomes 'go' (both can mean energy or enthusiasm).
'on' says to put letters next to each other.
'wife' becomes 'w'.
'new' becomes 'n'.
'go'+'w'+'n'='GOWN'
(Other definitions for gown that I've seen before include "An evening dress" , "Academic or formal wear" , "Ball dress" , "Academic (or evening) wear" , "Loose flowing garment for woman or judge" .)