Fabled sunken land (8)
I believe the answer is:
atlantis
'fabled sunken land' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for atlantis that I've seen before include "Fabled lost island" , "Legendary vanished island - mythical place" , "Legendary lost continent" , "Place of legend" , "Fabled sunken city" .)