Failing in duty of reconstruction of one tunnel - QED! (10)
I believe the answer is:
delinquent
'failing in duty of reconstruction' is the definition.
'delinquent' can be an answer for 'failing' (thesaurus). I'm not sure about the 'in duty of reconstruction' bit.
'of one tunnel qed' is the wordplay.
'of' indicates an anagram (the answer comes from or 'of' the letters).
'one' becomes 'i' (Roman numeral).
'i'+'tunnel'+'qed'='itunnelqed'
'itunnelqed' anagrammed gives 'DELINQUENT'.
Can you help me to learn more?
(Other definitions for delinquent that I've seen before include "Young offender" , "guilty of a minor offence" , "Neglectful of duty" , "SECOND PART OF 22" , "Offender, maybe juvenile" .)