On the Thames, this piece of land has its worth (4)
I believe the answer is:
isle
'on the thames this piece of land has its worth' is the definition.
'isle' can be an answer for 'piece' (I have seen 'Piece of land' mean 'isle' so perhaps 'piece' could also mean 'isle'). I am not sure about the remainder of the definition.
This is the entire clue.
Can you help me to learn more?
(Other definitions for isle that I've seen before include "Small seabound place" , "Land surrounded entirely by water" , "Eg, Sheppey" , "Christmas or Easter, perhaps" , "Prince Edward perhaps" .)