unclear (adj.)youdaoicibaDictYouDict[unclear 词源字典]
c. 1300, "not easy to understand," from un- (1) "not" + clear (adj.). Similar formation in Middle Dutch onclaer, Dutch onklaar, German unklar, Old Norse uklarr, Danish uklar, Swedish oklar. Of persons, in sense of "uncertain, doubtful," it is recorded from 1670s.[unclear etymology, unclear origin, 英语词源]