Piece of land is on lease (5)
I believe the answer is:
islet
'piece of land' is the definition.
(I've seen this before)
'is on lease' is the wordplay.
'on' says to put letters next to each other.
'lease' becomes 'let' (synonyms).
'is'+'let'='ISLET'
(Other definitions for islet that I've seen before include "Eyot, key" , "Minor key" , "small key?" , "Detached bit of land" , "Ait or key" .)