There’s one silly old icon (4)
I believe the answer is:
idol
'icon' is the definition.
(I've seen this before)
'there's one silly old' is the wordplay.
'there's' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'silly' indicates anagramming the letters.
'old' is an anagram of 'dol'.
'i'+'dol' is 'IDOL'.
(Other definitions for idol that I've seen before include "Heathen god" , "Who's greatly respected" , "Object of reverence" , "Worshipped figure (not painting); revered person" , "A graven image, or a hero" .)