title_body: What is opposite of "burzum", "darkness", in Tolkien's Black Speech?
upvoted_answer: As @Darkgamma says, we don't know.  The closest we have would probably be ghâsh, which means fire, and one could probably guess that the characteristic of being fire-like would be something like ghâshum, but there is no empirical evidence for that, except that the suffix -um seems to mean -ness, as in burz- (meaning dark) + -um (meaning -ness), put together to form burzum.
  
  That said, ghâshum would literally mean "the characteristic of being like fire," not literally "lightness."