Mass of glue! (4)
I believe the answer is:
size
I believe this is a double definition.
'mass' is the first definition.
(thesaurus)
'glue' is the second definition.
(I've seen this before)
'of' acts as a link.
(Other definitions for size that I've seen before include "gelatinous mixture" , "Dimensions, magnitude" , "Measure" , "mass" , "Dimension" .)