Boil over two months, late in the year (6)
I believe the answer is:
decoct
'boil over two months' is the definition.
'decoct' can be an answer for 'boil' (decocting is a kind of boiling). I'm not certain of the 'over two months' bit.
'late in the year' is the wordplay.
'late' becomes 'dec'.
'in the year' becomes 'oct' (I can't explain this - if you can you should believe this answer much more).
'dec'+'oct'='DECOCT'
Can you help me to learn more?
(Other definitions for decoct that I've seen before include "Extract essence from (archaic)" , "extract by boiling" , "herbal extract" .)