In one unit of land, see another! (4)
I believe the answer is:
acre
'land see another' is the definition.
I can't judge whether this definition defines the answer.
'in one unit' is the wordplay.
'in' means one lot of letters goes inside another.
'one' becomes 'ace' (synonyms).
'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" .)