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' indicates the answer is hidden within the clue.
'EDGE' is hidden in the letters of 'bed generally'.
(Other definitions for edge that I've seen before include "Advantage (informal)" , "Border - advantage" , "Rim, lip" , "Sharpness of mind" , "Rim,border" .)