Last female deer succeeded initially in annual test (8)
I believe the answer is:
'last' is the definition.
(I've seen this before)
'female deer succeeded initially in annual test' is the wordplay.
'female deer' becomes 'hind' (I've seen this in another clue).
'initially' indicates taking the first letters.
'in' is an insertion indicator.
'annual test' becomes 'MOT' (Ministry of Transport test).
The initial letter of 'succeeded' is 's'.
's' inserted inside 'mot' is 'most'.
(Other definitions for hindmost that I've seen before include "after all the others" , "The one who is furthest behind - devil take him" , "Last" , "One at the back (devil take him!)" , "Like a tail-ender" .)