Fall mo. (3)
(Other definitions for oct that I've seen before include "10th month (abbrev.)" , "Month, in short" .)
'fall mo' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sept that I've seen before include "Short month" , "Month (abbreviation); clan subdivision (in Ireland)" , "Thirty days" , "Division of a tribe in Ireland or Scotland" , "Part of clan" .)