Chicken in vessel crossing river (5)
I believe the answer is:
capon
'chicken' is the definition.
(I know that capon is a type of chicken)
'vessel crossing river' is the wordplay.
'vessel' becomes 'can' (type of container).
'crossing' indicates putting letters inside (to cross can mean to go over or around).
'river' becomes 'po' (Italian river).
'can' enclosing 'po' is 'CAPON'.
'in' acts as a link.
(Other definitions for capon that I've seen before include "fowl fattened for pot" , "Emasculated fowl" , "Castrated male chicken" , "Male chicken for eating" , "Castrated rooster fattened for eating" .)