European twice collared by West End vagrant calmed down (9)
I believe the answer is:
sweetened
'calmed down' is the definition.
(sweeten can mean to calm or appease someone)
'european twice collared by west end vagrant' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'twice' indicates the doubling of some letters.
'collared by' means one lot of letters goes inside another (I've seen this in other clues).
'vagrant' is an anagram indicator (I've seen this in other clues).
'e' duplicated is 'ee'.
'west'+'end'='westend'
'westend' is an anagram of 'swtened'.
'ee' inserted within 'swtened' is 'SWEETENED'.
(Other definitions for sweetened that I've seen before include "Made less sour" , "Added sugar" , "Sugared" , "Made agreeable" .)