Left-over rail used in construction (8)
I believe the answer is:
residual
'construction' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'left-over rail used' is the wordplay.
'rail used' can be anagrammed to 'RESIDUAL'.
Though, I'm unsure how the anagram is indicated.
'in' is the link.
Can you help me to learn more?
(Other definitions for residual that I've seen before include "Remaining at the end" , "Left over as a remainder" , "unused" , "Leftover - used rail (anag)" , "Remaining; repeat royalty" .)