Without doctor filling shift for a month (8)
I believe the answer is:
november
'a month' is the definition.
(November is a month)
'without doctor filling shift for' is the wordplay.
'without' becomes 'no'.
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'filling' is an insertion indicator.
'shift for' becomes 'veer' (I can't explain this - if you can you should give a lot more credence to this answer).
'mb' put into 'veer' is 'vember'.
'no'+'vember'='NOVEMBER'
(Other definitions for november that I've seen before include "Never mob (anag.)" , "when Christmas is getting near" , "Guy Fawkes month" , "Thirty days hath September, April, June and . . . . . . . ." , "Ninth month in the Roman calendar" .)