Piece of furniture, one skirted by cleaner (5)
I believe the answer is:
Here is my best explanation:
'piece of furniture' is the definition.
(chair is a kind of piece of furniture)
'one skirted by cleaner' is the subsidiary indication.
'one' becomes 'i' (roman numeral).
'skirted by' means one lot of letters goes inside another (\'skirt\' can mean \'circle\' or \'go around\').
'cleaner' becomes 'char' (char is a kind of cleaner).
'i' put within 'char' is 'chair'.
(Other definitions for chair that I've seen before include "Senior academic post", "Item of furniture (which can be addressed!)", "Official position of authority", "control meeting", "See 4", "Head of a university faculty or department", "The top committee seat", "Supporter", "Seat (of learning?)" and "Get seat".)