Glue is finished by end of tube (5)
I believe the answer is:
paste
'glue' is the definition.
('paste' can be a synonym of 'glue')
'finished by end of tube' is the wordplay.
'finished' becomes 'past'.
'by' means one lot of letters go next to another.
'end of' says to take the final letters.
The final letter of 'tube' is 'e'.
'past'+'e'='PASTE'
'is' is the link.
(Other definitions for paste that I've seen before include "Watery cement" , "Dough - adhesive - gem substitute" , "Fake gems; adhesive" , "An adhesive, or material for artificial gems" , "Hit" .)