Unclear

wiktionary

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From Middle English unclere, equivalent to un- +‎ clear. Compare Saterland Frisian uunkloor(“unclear”), West Frisian ûnklear(“inoperative, broken”), Dutch onklaar(“out of order, defective, broken”), German unklar(“unclear”), Danish uklar(“unclear”), Swedish oklar(“unclear”).

etymonline

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unclear (adj.)

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.