Memorial Day month (3)
I believe the answer is:
may
'memorial day month' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for may that I've seen before include "Month; hawthorn" , "Might" , "The Darling Buds of - (H. E. Bates)" , "Month - tree" , "The permissive month" .)