Measure of land, note, in a confined space (7)
I believe the answer is:
Here is my best explanation:
'measure of land' is the definition.
(I've seen this before)
'note in a confined space' is the subsidiary indication.
'note' becomes 're'.
'in' indicates putting letters inside.
'confined space' becomes 'cage' (I've seen this before).
're' inserted within 'acage' is 'acreage'.
(Other definitions for acreage that I've seen before include "good quantity of land", "Surface area", "Amount of land", "Measure used by farmer", "Farm", "amount", "plot", "Area measure", "Land area" and "measure of land".)