An Etymological Dictionary of the German Language/Annotated/siedeln
siedeln, verb, ‘to settle, establish,’ from the equivalent Middle High German sidelen; allied to Middle High German sëdel, Old High German sëdal, masculine and neuter, ‘seat, settle, residence,’ a variant of Sessel, Gothic sitls (*siþls). There are several examples of the change of tl to þl (parallel to that of tn to þn in Boden). Compare also Einsiedel.