IPA: /ˌʌnɪkˈspleɪnd/
KK: /ʌnɪk'spleɪnd/
Something that is not clarified or understood, often leaving people puzzled about its cause or reason.
The sudden disappearance of the plane remains unexplained after all these years.
Unexplained → It is formed from "un-" (meaning not) and "explained" (from Latin "explanare", meaning to make clear or to explain). The word "unexplained" means not made clear or not clarified.
Think of 'not' ('un-') making something 'clear' ('explanare') — that's why unexplained means something that is not clear.