After that, engineers became genuine (7)
I believe the answer is:
sincere
'genuine' is the definition.
(sincere can mean authentic or genuine)
'after that engineers' is the wordplay.
'after' becomes 'since' (since can mean after a certain time).
'that engineers' becomes 're' (Royal Engineers).
'since'+'re'='SINCERE'
'became' is the link.
(Other definitions for sincere that I've seen before include "Earnest" , "Candid" , "True" , "Honest, frank" , "like informal correspondents?" .)