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.
Meanings
(rare) Neat and orderly.
1610: John Marston, Histrio-Mastix, page 28 (quarto): [Perpetuana:] Nay Ile be matchlesse for a carckanet,/Whose Pearles and Diamonds plac'd with ruly rocks/Shall circle this faire necke to set it forth [.]
What is certain is that everything they see is strange: the lifeless neatness of the courtyard, the straightness of the paths, the ruly gang of labourers in their dull uniforms and with their ageless, polished faces. 2022, Jim Crace, eden, Picador, page 224: