Slime (3)
I believe the answer is:
goo
'slime' is the definition.
(synonyms)
This is all the clue.
(Other definitions for goo that I've seen before include "syrup" , "Sticky wet material or sickly sentiment" , "Sentimentality (sl.)" , "Sticky and slimy stuff" , "Sticky substance (colloq.)" .)