unexplained

adj

Etymology: Etymology tree English un- English explained English unexplained From un- + explained.

1. Not explained; of unknown cause or origin.

   “Why this already very fast train should be speeded up still further, when none of the other more easily timed S.R. West of England trains has a single minute pared from its schedule, is unexplained - unless this is a playful dig at the Western Region, most of whose expresses, by reason of additional stops, will be decelerated from the same date.”