To break an egg can be a sticky mess (3)
I believe the answer is:
goo
'a sticky mess' is the definition.
(thesaurus)
'to break an egg' is the wordplay.
'to break' becomes 'go' ('go' can be a synonym of 'break').
'an egg' becomes 'o' (I've seen this in other clues).
'go'+'o'='GOO'
'can be' acts as a link.
(Other definitions for goo that I've seen before include "Sticky substance (sl.)" , "syrup" , "mud, for example" , "Sticky wet material or sickly sentiment" , "Anything sticky" .)