unexplained
1. [ adjective ] not explained
Examples:

"accomplished by some unexplained process"

Related terms: undetermined
2. [ adjective ] having the reason or cause not made clear
Examples:

"an unexplained error"

Related terms: inexplicable
Similar spelling:   unexplainable
  unexpired
  unexplored
  unexploded
  unexploited
  unexpended
  unexpected
  unexpressed
  unexpectedly