The Collaborative International Dictionary of English v.0.48:

Viscous \Vis"cous\, a. [L. viscosus. See Viscid.]
   Adhesive or sticky, and having a ropy or glutinous
   consistency; viscid; glutinous; clammy; tenacious; as, a
   viscous juice. -- Vis"cous*ness, n.
   [1913 Webster]

   Note: There is no well-defined distinction in meaning between
         viscous and viscid.
         [1913 Webster]

WordNet (r) 3.0 (2006):

viscous
    adj 1: having a relatively high resistance to flow [syn:
           syrupy, viscous]
    2: having the sticky properties of an adhesive [syn: gluey,
       glutinous, gummy, mucilaginous, pasty, sticky,
       viscid, viscous]