Bank official rings Head of Eurobank (4)
I believe the answer is:
reef
'bank' is the definition.
(I've seen this before)
'official rings head of eurobank' is the wordplay.
'official' becomes 'ref' (match official in football, say).
'rings' indicates putting letters inside (some letters are ringed or contained by others).
'head of' says to take the initial letters.
The initial letter of 'eurobank' is 'e'.
'ref' enclosing 'e' is 'REEF'.
(Other definitions for reef that I've seen before include "Rock near water's surface" , "Rocky ridge near sea surface" , "Ridge of rock or sand just below sea surface" , "Ridge of rock just below ocean surface" , "Type of knot" .)