Lack of interest in a course leading to the unknown (6)
I believe the answer is:
apathy
'lack of interest' is the definition.
'a course leading to the unknown' is the wordplay.
'course' becomes 'path' ('path' can be a synonym of 'course'**).
'leading to' is a charade indicator (letters next to each other) (some letters go before or lead others).
'the unknown' becomes 'y' (algebra).
'a'+'path'+'y'='APATHY'
'in' acts as a link.
(Other definitions for apathy that I've seen before include "Indifference, emotionlessness" , "Absense of interest or emotion" , "Indifference - listlessness" , "Absence of emotion or enthusiasm" , "Lack of interest in things in general" .)