Freight firm holding a case of Riesling (5)
I believe the answer is:
cargo
'freight' is the definition.
(synonyms)
'firm holding a case of riesling' is the wordplay.
'firm' becomes 'co' (abbreviation for company).
'holding' means one lot of letters goes inside another.
'case of' means to remove the middle letters (like emptying a case).
'riesling' with its middle removed is 'rg'.
'a'+'rg'='arg'
'co' enclosing 'arg' is 'CARGO'.
(Other definitions for cargo that I've seen before include "What gets carried" , "Goods carried by vessel or vehicle" , "Freight, load" , "Ship's freight" , "Consignment" .)