Black's Law Dictionary (revised 4 ed.; the most recent is 12 ed. but I don't have a copy- if anyone has a newer edition, I'd be curious to see if it still aligns), which is generally to be aligned and authoritative and even the "gold standard" for defining terminology in the legal wheelhouse, defines "illegal" as: ILLEGAL. Not authorized by law; illicit; unlawful; contrary to law; Protest of Downing, 164 Okl. 181, 23 P.2d 173. *Sometimes this term means merely that which lacks authority of or support from law; but more frequently it imports a violation. Etymologically, the word seems to convey the negative meaning only. But in ordinary use it has a severer, stronger signification; the idea of censure or condemnation for breaking law is usually presented. But the law implied in illegal is not necessarily an express statute. Things are called "illegal" for a violation of commonlaw principles. And the term does not imply that the act spoken of is immoral or wicked; it implies only a breach of the law. Tiedt v. Carstensen, 61 Iowa, 334, 16 N.W. 214.* Which *seems* fine and dandy and pretty clear until you get to the 1 1/3 page definition of "law", summarized as: LAW. That which is laid down, ordained, or established. A rule or method according to which phenomena or actions co-exist or follow each other. That which must be obeyed and followed by citizens, subject to sanctions or legal consequences, is a "law." Koenig v. Flynn, 258 N.Y. 292, 179 N. E. 705. (...) "Lawful", however, is a little more helpful in the discussion: LAWFUL. Legal; warranted or authorized by the law; having the qualifications prescribed by law; not contrary to nor forbidden by the law. Ohio Automatic Sprinkler Co. v. Fender, 108 Ohio St. 149, 141 N.E. 269, 275; McDonnell v. Murnan Shipbuilding Corporation, 210 Ala. 611, 98 So. 887, 889; Hafner Mfg. Co. v. City of St. Louis, 262 Mo. 621, 172 S.W. 28, 33. *The principal distinction between the terms "lawful" and "legal" is that the former contemplates the substance of law, the latter the form of law. To say of an act that it is "lawful" implies that it is authorized, sanctioned, or at any rate not forbidden, by law. To say that it is "legal" implies that it is done or performed in accordance with the forms and usages of law, or in a technical manner. In this sense "illegal" approaches the meaning of "invalid." For example, a contract or will, executed without the required formalities, might be said to be invalid or illegal, but could not be described as unlawful. Further, the word "lawful" more clearly implies an ethical content than does "legal." The latter goes no further than to denote compliance, with positive, technical, or formal rules; while the former usually imports a moral substance or ethical permissibility. A further distinction is that the word "legal" is used as the synonym of "constructive," which "lawful" is not. Thus "legal fraud" is fraud implied or inferred by law, or made out by construction. "Lawful fraud" would be a contradiction of terms. Again, "legal" is used as the antithesis of "equitable." Thus, we speak of "legal assets," "legal estate," etc., but not of "lawful assets," or "lawful estate." But there are some connections in which the two words are used as exact equivalents. Thus, a "lawful" writ, warrant, or process is the same as a "legal" writ, warrant, or process.* (*emphasis* added)