Large bed size (4)
I believe the answer is:
king
'large bed size' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for king that I've seen before include "See 23 Down" , "Legendary monarch" , "and 21 Across: Shakespeare play" , "Recipient of 10 21 [VELODROME GOLD]" , "eg Wenceslas" .)