Of exceptional size (7)
I believe the answer is:
titanic
'of exceptional size' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for titanic that I've seen before include "Of enormous size, like the stricken liner" , "Giant" , "Famously sunken ship" , "Ship sunk by iceberg" , "Huge - disaster struck this ship" .)