unexplained
/ˌʌnɪkˈspleɪnd/adjective
1- not described or made clear; unknown莫名其妙的; 不明确的：
the reason for her summons was as yet unexplained.
她召见的原因至今尚不清楚。
1.1
- not accounted for or attributable to an identified cause未解释的; 原因不明的：
cot death is still an unexplained phenomenon.
婴儿猝死仍是一种无法解释的现象。