Strip of land (7)
I believe the answer is:
isthmus
'strip of land' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for isthmus that I've seen before include "Narrow neck of land joining two larger portions" , "Narrow linking piece of land" , "Neck of land between two seas" , "Narrow strip of land between two larger ones" , "Narrow land bridge" .)