Engineers interrupting popular exam, showing curiosity (8)
I believe the answer is:
interest
'curiosity' is the definition.
(I know that curiosity can be written as interest)
'engineers interrupting popular exam' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'interrupting' indicates putting letters inside.
'popular' becomes 'in' ('in' can mean trendy).
'exam' becomes 'test' (synonyms).
'in'+'test'='intest'
're' put into 'intest' is 'INTEREST'.
'showing' acts as a link.
(Other definitions for interest that I've seen before include "Principal" , "thing" , "Money paid on a loan" , "Money paid on deposit account or loans" , "Sum of money paid on top of borrowed amount" .)