The Collaborative International Dictionary of English v.0.48:

Slugabed \Slug"a*bed`\, n.
   One who indulges in lying abed; a sluggard. [R.] "Fie, you
   slugabed!" --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

slugabed
    n 1: a person who stays in bed until a relatively late hour
         [syn: lie-abed, slugabed]