Husband going astray? Something fishy here (7)
I believe the answer is:
herring
'astray? something fishy here' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'husband going' is the wordplay.
'husband' becomes 'h'.
'going' becomes 'erring' (erring is a kind of going).
'h'+'erring'='HERRING'
(Other definitions for herring that I've seen before include "Fish that can be red and kippered!" , "Fish of northern waters, can be salted or pickled" , "Fatty fish" , "Sea fish" , "Small silvery fish" .)