Measure of land, note, in a confined space (7)
'measure of land' is the definition.
(I've seen this before)
'note in a confined space' is the wordplay.
'note' becomes 're' (**).
'in' is an insertion indicator.
'confined space' becomes 'cage' (I've seen this before).
're' going inside 'acage' is 'ACREAGE'.
(Other definitions for acreage that I've seen before include "expanse", "plot", "Surface area", "Measure of land", "Measure used by farmer".)