In The Zoo, part of the back door is missing second lock and the odd stall? (6)
I believe the answer is:
dorsal
'in the zoo part of the back door' is the definition.
I can't tell whether this defines the answer.
'missing second lock and the odd stall?' is the wordplay.
'missing second lock' becomes 'dor' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other).
'the odd' indicates alternate letters.
The alternating letters of 'stall' are 'sal'.
'dor'+'sal'='DORSAL'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for dorsal that I've seen before include "Kind of fin" , "On the upper back" , "(Of fin) on upper side" , "'On the back, a fin on a fish perhaps (6)'" , "On the back, fin on a fish say" .)