Month to get brown in 45 degrees (6)
I believe the answer is:
octant
'45 degrees' is the definition.
(I've seen this before)
'month to get brown' is the wordplay.
'month' becomes 'oct' (abbreviation for October).
'to get' indicates putting letters inside.
'brown' becomes 'tan' (tan is a kind of brown).
'oct' enclosing 'tan' is 'OCTANT'.
'in' acts as a link.
(Other definitions for octant that I've seen before include "45 degrees" , "segment of disc" , "Device to measure angles to a celestial body" , "Eighth part of circle" .)