A month of the year (6)
(Other definitions for august that I've seen before include "Month named after a Roman emperor" , "clown in circus" , "Gregorian calendar month" , "A grand month?" , "when students are down?" .)
'a month of the year' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for april that I've seen before include "Start of the second quarter" , "Woman" , "days on end" , "Month that's autumnal in Oz" , "Traditionally showery month" .)