Piece of land is over half a mile (4)
I believe the answer is:
isle
'piece of land' is the definition.
(I've seen this before)
'is over half a mile' is the wordplay.
'over' says to put letters next to each other.
'half a' indicates taking half.
'mile' halved is 'le'.
'is'+'le'='ISLE'
(Other definitions for isle that I've seen before include "The Emerald - (Ireland)" , "description of Britain" , "Capri for one" , "'There is an ..., a bonny ...' (rugby anthem in the South)" , "eg Man, Dogs" .)