Because engineers are worthy of credit (7)
I believe the answer is:
sincere
'worthy of credit' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
'because engineers' is the wordplay.
'because' becomes 'since' (I've seen this before).
'engineers' becomes 're' (abbreviation for Royal Engineers).
'since'+'re'='SINCERE'
'are' is the link.
Can you help me to learn more?
(Other definitions for sincere that I've seen before include "Free from deceit" , "Earnest" , "devout" , "Candid" , "Without deceit, genuine" .)