Gathering in a ship with euro to gamble at sea (10)
I believe the answer is:
assemblage
'gathering' is the definition.
(I know that gathering can be written as assemblage)
'a ship with euro to gamble at sea' is the wordplay.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'with' is a charade indicator (letters next to each other).
'euro' becomes 'E' (E resembles the Euro symbol).
'to' says to put letters next to each other.
'at sea' is an anagram indicator.
'gamble' is an anagram of 'mblage'.
'a'+'ss'+'e'+'mblage'='ASSEMBLAGE'
'in' acts as a link.
(Other definitions for assemblage that I've seen before include "congregation" , "Group" , "Collection (of things or people)" , "collection is made" , "Collection, gathering" .)