Unforgettable (6)
(Other definitions for iconic that I've seen before include "admired type" , "Widely-recognised" , "conventional type" , "Relating to religious pictures" , "Culturally representative" .)
'unforgettable' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for indelible that I've seen before include "Cannot be removed or erased" , "fixed" , "Of mark or stain, unable to be rubbed out" , "Of stain, unable to be removed" , "Permanent" .)