Nasty European retaining secure check (8)
I believe the answer is:
blockade
'check' is the definition.
(thesaurus)
'nasty european retaining secure' is the wordplay.
'nasty' becomes 'bad' (I've seen this in another clue).
'european' becomes 'E' (abbreviation e.g. EU).
'retaining' means one lot of letters goes inside another (inserted letters are held or retained).
'secure' becomes 'lock' (locking is a kind of securing).
'bad'+'e'='bade'
'bade' going around 'lock' is 'BLOCKADE'.
(Other definitions for blockade that I've seen before include "Physical prevention of access" , "Military restriction of access" , "Obstruction of access, as to entry of goods" , "Isolation of place by sea" , "Seal off (a sea port)" .)