Leave out of room itself (4)
I believe the answer is:
Here is my best explanation:
'leave out' is the definition.
('omit' can be a synonym of 'leave out')
'of room itself' is the subsidiary indication.
'of' indicates a hidden word.
'omit' is hidden within 'room itself'.
(Other definitions for omit that I've seen before include "Leave out or overlook", "Exclude; veto", "Drop", "Leave something out", "Fail (to do something)", "Fail to mention", "Leave out or fail to do", "Leave out, perhaps in error", "Don't include" and "Disregard".)