Adult very quiet with fish near (8)
I believe the answer is:
approach
'near' is the definition.
(synonyms)
'adult very quiet with fish' is the wordplay.
'adult' becomes 'a' (abbreviation).
'very quiet' becomes 'pp' (musical abbreviation for pianissimo).
'with' is a charade indicator (letters next to each other).
'fish' becomes 'roach' (roach is a kind of fish).
'a'+'pp'+'roach'='APPROACH'
(Other definitions for approach that I've seen before include "driveway" , "Go towards" , "Draw near or nearer to" , "Speak to" , "Offer" .)