Month lost in major reversal: Everyman's drunk wine (5)
I believe the answer is:
rioja
'wine' is the definition.
(I know that Rioja is a type of red wine)
'month lost in major reversal everyman's drunk' is the wordplay.
'month' becomes 'M' (standard abbreviation).
'lost in' suggests deleting specific letters.
'reversal' says the letters should be written in reverse.
'everyman' becomes 'i' (where 'Everyman' is the setter of the crossword).
'drunk' is an insertion indicator (inserted letters are drunk in).
'major' with 'm' taken out is 'ajor'.
'ajor' in reverse letter order is 'roja'.
'roja' placed around 'i' is 'RIOJA'.
(Other definitions for rioja that I've seen before include "Popular Spanish wine" , "Spanish red wine" , "Open space (ancient Greek)" , "Spanish wine variety" , "Spanish wine type" .)