State low to seize returning vessel (6)
I believe the answer is:
monaco
'state' is the definition.
(Monaco is an example)
'low to seize returning vessel' is the wordplay.
'low' becomes 'moo' ('moo' can be a synonym of 'low').
'to seize' is an insertion indicator.
'returning' shows that the letters should be reversed in order.
'vessel' becomes 'can' (I've seen this before).
'can' written backwards gives 'nac'.
'moo' going around 'nac' is 'MONACO'.
(Other definitions for monaco that I've seen before include "Monte Carlo country" , "Principality of the Rainiers" , "Home of the Grimaldis" , "Constitutional monarchy on the French Riviera" , "Oman Co. (anag)" .)