Unriddle comes from un- ('reversal, undoing') + riddle, from Old English rǣdels(e) ('opinion, riddle'), from rǣdan ('to advise, interpret'). The historical chain includes Old English un- and Old English rǣdels. The quoted older senses, "reversal, undoing", "opinion, riddle", and "to advise, interpret", supply the semantic anchors for unriddle. The formation is best read as compound and borrowed: the word unriddle carries its older form-history into a compact English lexical shape. In present English it is used as a verb, "to solve or explain a riddle, puzzle, or mystery". English derivatives include unriddler; related English forms include riddle. The result is a verb whose etymology preserves both the older form and the later English specialization.