Rest within generally contents (5)
I believe the answer is:
hinge
'rest' is the definition.
(thesaurus)
'within generally contents' is the wordplay.
'contents' says the answer is hidden in the clue (I've seen 'content of' mean this).
'HINGE' is hidden in the letters of 'within generally'.
(Other definitions for hinge that I've seen before include "Moving joint" , "door open because of this?" , "hang" , "Key principle" , "Part of a door" .)