Many have to be cut short (4)
I believe the answer is:
Here is my best explanation:
'be cut short' is the definition.
'many have' is the subsidiary indication.
'many' becomes 'm'.
'have' becomes 'own' ('own' can be a synonym of 'have').
'to' is the link.
(Other definitions for mown that I've seen before include "Block of cast metal", "Cut down with a blade" and "(Of grass) cut".)