Join head of retail bank (4)
I believe the answer is:
tier
'bank' is the definition.
(I've seen this before)
'join head of retail' is the wordplay.
'join' becomes 'tie' (I've seen this before).
'head of' indicates taking the first letters.
The first letter of 'retail' is 'r'.
'tie'+'r'='TIER'
(Other definitions for tier that I've seen before include "he hasn't won?" , "Row in theatre" , "Row, level" , "Wedding cake feature" , "range" .)