Progress made in one month (5)
I believe the answer is:
march
This clue is a double definition.
'progress' is the first definition.
(I know that march is a type of progress)
'one month' is the second definition.
(I know that Gregorian calendar month is a type of calendar month)
'made in' acts as a link.
(Other definitions for march that I've seen before include "Walk smartly" , "Military walking style" , "that happens fairly early each year" , "Spring" , "Proceed in procession" .)