Is lonely only having left land (4)
I believe the answer is:
isle
'land' is the definition.
(isle is a kind of land)
'is lonely' is the wordplay.
'lonely' becomes 'le' (I can't justify this - if you can you should give a lot more credence to this answer).
'is'+'le'='ISLE'
'only having left' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for isle that I've seen before include "isolated spot" , "See 10 Down" , "Eg, Iona" , "The Emerald - (Ireland)" , "Body of land surrounded by water" .)