Source : Webster's Revised Unabridged Dictionary (1913)

Obelus \Ob"e*lus\, n.; pl. {Obeli}. [L., fr. Gr. 'obelo`s,
   prop., a spit.] (Print.)
   A mark [thus ---, or /]; -- so called as resembling a needle.
   In old MSS. or editions of the classics, it marks suspected
   passages or readings.