Project in book glue spoiled (5)
I believe the answer is:
bulge
'project' is the definition.
(I know that bulge is a type of project)
'book glue spoiled' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'spoiled' indicates an anagram.
'glue' is an anagram of 'ulge'.
'b'+'ulge'='BULGE'
'in' is the link.
(Other definitions for bulge that I've seen before include "Swell" , "Rounded swelling" , "surge?" , "Protrude" , "Swelling - sudden increase" .)