Symbol in holding company (4)
I believe the answer is:
icon
'symbol' is the definition.
(I know that icon is a type of symbol)
'in holding company' is the wordplay.
'holding' means one lot of letters goes inside another.
'company' becomes 'co' (abbreviation).
'in' placed around 'co' is 'ICON'.
(Other definitions for icon that I've seen before include "Religious picture on a wooden panel" , "Religious painting or symbol on computer screen" , "Representation, religious say" , "Symbol activated by mouse" , "Adored person" .)