Gunge (3)
I believe the answer is:
goo
'gunge' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for goo that I've seen before include "Sticky matter" , "Substance that's viscous" , "Sticky and slimy stuff" , "Sticky wet material or sickly sentiment" , "Sticky substance (colloq.)" .)