Engineers jamming bug covertly (2,6)
I believe the answer is:
in secret
'covertly' is the definition.
(I've seen this in another clue)
'engineers jamming bug' is the wordplay.
I cannot quite see how this works, but
'engineers' could be 're' (abbreviation for Royal Engineers) and 're' is found in the answer.
'bug' could be 'insect' (bug can mean an insect) and 'insect' is found within the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for in secret that I've seen before include "sub rosa" , "Without others knowing" , "Covertly" , "behind closed doors" , "Not openly stated" .)