Gigantic statue that once stood at the harbour entrance at Rhodes (8)
I believe the answer is:
colossus
'gigantic statue that once stood at the harbour entrance at rhodes' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for colossus that I've seen before include "Giant statue once at Rhodes" , "A giant figure - there once was one at Rhodes" , "Great thing" , "huge figure" , "Something larger than life" .)