In one unit of land, see another! (4)
I believe the answer is:
acre
'land see another' is the definition.
I can't tell whether this defines the answer.
'in one unit' is the wordplay.
'in' is an insertion indicator.
'one' becomes 'ace' (ace has a value of one in some card games).
'unit' becomes 'r' (R is an example).
'ace' enclosing 'r' is 'ACRE'.
'of' is the link.
Can you help me to learn more?
(Other definitions for acre that I've seen before include "Imperial land measure" , "Site of battle" , "Old unit of area - old port" , "Care about this bit of land" , "Ancient city in Israel" .)