Syrupy (7)
I believe the answer is:
viscous
'syrupy' is the definition.
(I know that syrupy can be written as viscous)
This is all the clue.
(Other definitions for viscous that I've seen before include "Resistant to flow" , "Gelatinous" , "Thick and gluey, like heavy oil" , "Thick, sticky (liquid)" , "Treacly" .)