From The Collaborative International Dictionary of English v.0.48 [gcide]:
2. A rule established by authority; a permanent rule of action; a statute, law, regulation, rescript, or accepted usage; an edict or decree; esp., a local law enacted by a municipal government; as, a municipal ordinance.
Note: Acts of Parliament are sometimes called ordinances; also, certain colonial laws and certain acts of Congress under Confederation; as, the ordinance of 1787 for the government of the territory of the United States northwest of the Ohio River; the colonial ordinance of 1641, or 1647. This word is often used in Scripture in the sense of a law or statute of sovereign power. --Ex. xv. 25. --Num. x. 8. --Ezra iii. 10. Its most frequent application now in the United States is to laws and regulations of municipal corporations. --Wharton (Law Dict.).
From WordNet (r) 3.0 (2006) [wn]:
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