Posh sons in boat cut fare from Japan (5)
I believe the answer is:
sushi
'fare from japan' is the definition.
(I've seen this before)
'posh sons in boat cut' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'sons' becomes 'ss' (s is abbreviation for son).
'in' means one lot of letters goes inside another.
'boat cut' becomes 'hi' (I am not sure about this - if you are sure you should believe this answer much more).
'u' put inside 'ss' is 'sus'.
'sus'+'hi'='SUSHI'
Can you help me to learn more?
(Other definitions for sushi that I've seen before include "Exotic food" , "Japanese vinegared rice dish" , "Raw fish dishes" , "Japanese rice-based dish" , "cold food" .)