River delta where peas grow (3)
I believe the answer is:
pod
'where peas grow' is the definition.
(I've seen this before)
'river delta' is the wordplay.
'river' becomes 'po' (Italian river).
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'po'+'d'='POD'
(Other definitions for pod that I've seen before include "Fruit of a legume" , "A seedcase; some whales" , "A pea grows in it" , "Long seed case" , "Seed carrier (eg, pea)" .)