Old English; earliest use found in Old English Martyrology. Cognate with or formed similarly to Old Frisian unriuchtlike (West Frisian ûnrjochtlik), Middle Dutch onrechtelīke (Dutch †onrechtelijk), Middle Low German unrechteliken, Old High German unrehtlīhho (Middle High German unrehtlīche, German unrechtlich), Old Icelandic úréttliga, Old Danish wraettelighe, vreteligh, uraetaelich (Danish urettelig, now rare), Old Swedish orätlika from the Germanic base of un- + the Germanic base of rightly.