Rarely seen part of the French president's residence (6)
I believe the answer is:
elysee
'the french president's residence' is the definition.
(I've seen this in another clue)
'rarely seen part' is the wordplay.
'part' indicates the answer is hidden within the clue.
'ELYSEE' is hidden in the letters of 'rarely seen'.
'of' acts as a link.
(Other definitions for elysee that I've seen before include "Official palace in Paris" , "Parisian palace" , "- Palace, French presidential residence" , "Palace occupied by the French president" , "French President's palace" .)