ruly

From Middle English rewly, ruly, rewely, reweliche, from Old English hrēowlīċ (“grievous, pitiful, sad, wretched, cruel”), equivalent to rue + -ly.

Back-formation from unruly, or perhaps a continuation of Middle English rewly, ruly, reuli (“subject to a religious rule, regular”), equivalent to rule + -ly, rule + -y; or perhaps from Old French rulé, reulé, rieulé (“ruled”), past participle of rieuler (“to rule”). More at rule.

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