Side of the bed, generally (4)
I believe the answer is:
edge
'side' is the definition.
(edge is a kind of side)
'of the bed generally' is the wordplay.
'of' says the answer is hidden in the clue.
'EDGE' is hidden within 'bed generally'.
(Other definitions for edge that I've seen before include "Advantage (informal)" , "Border - advantage" , "Rim, lip" , "Sharpness of mind" , "Rim,border" .)