Sticky gunk (3)
I believe the answer is:
goo
'sticky gunk' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for goo that I've seen before include "syrup" , "Sticky substance (colloq.)" , "mud, for example" , "Sentimentality (sl.)" , "Sticky stuff or sickly sentiment" .)