Aspiration concerning blocking engineering project? (5)
I believe the answer is:
dream
'aspiration' is the definition.
(synonyms)
'concerning blocking engineering project?' is the wordplay.
'concerning' becomes 're'.
'blocking' is an insertion indicator.
'engineering project?' becomes 'dam' (a major engineering project).
're' put into 'dam' is 'DREAM'.
(Other definitions for dream that I've seen before include "Nocturnal vision" , "Reverie or nightmare" , "Aspiration" , "Think vaguely" , "Bedroom vision?" .)