Looking up debtor - a student - not quite lame duck (7)
I believe the answer is:
mallard
'duck' is the definition.
(mallard is a kind of duck)
'looking up debtor a student not quite lame' is the wordplay.
'looking up' is a reversal indicator.
'debtor' becomes 'dr'.
'student' becomes 'l' (as in L-plates for learner drivers).
'not quite' means to remove the last letter.
'lame' with its last letter taken away is 'lam'.
'dr'+'a'+'l'+'lam'='drallam'
'drallam' written backwards gives 'MALLARD'.
(Other definitions for mallard that I've seen before include "Ancestor of all domestic ducks" , "Engine holding the world speed record for a steam locomotive, set at 123mph in 1938" , "Oldest breed of duck" , "Kind of duck" , "Common wild duck" .)