Course covering constant alongside unknown variable (6)
I believe the answer is:
patchy
'variable' is the definition.
(thesaurus)
'course covering constant alongside unknown' is the wordplay.
'course' becomes 'path' (path can mean a route or course).
'covering' means one lot of letters goes inside another.
'constant' becomes 'c' (common symbol in maths for an unknown constant).
'alongside' is a charade indicator (letters next to each other).
'unknown' becomes 'y' (algebra).
'path' enclosing 'c' is 'patch'.
'patch'+'y'='PATCHY'
(Other definitions for patchy that I've seen before include "in an irregular way" , "Uneven, random" , "Uneven in quality - mended too often" , "Morose" , "Intermittent" .)