Most people understand "operating a motor vehicle" as driving, until they are arrested for DUI while sleeping off in their turned off car.
Most people understand "loaded weapon" as a gun with bullets in it, until they are charged in NYC with possession of a loaded firearm despite having the gun and the bullets in separate locked containers.
How far can such redefinitions of common words divert from the common usage?
Most pieces of legislation have a “dictionary” detailing, for the purposes of that legislation (or generally) what specific words and phrases mean. This can broaden (or narrow) the definition compared to how they are used in normal English.
The purpose of this is not to set a trap for the unwary, although this may happen, but to introduce precision and to allow a short defined term to be used in the drafting rather than having to explain what is meant verbosely every time it’s used.
Of course, they can’t redefine terms so that they give themselves jurisdiction when they otherwise wouldn’t have it. For example, in australia, the Constitution gives the Federal Parliament the power to make laws about, among other things, “external affairs”. A law that tried to define “external affairs” more broadly than the Constitution does (which it doesn’t, so we fall back on what it means in English) would be invalid.
The effective limit is whatever the courts will put up with. Legislatures can pass laws that will be overturned by the courts, so the real question is whether a redefinition will be upheld by the courts. It can be difficult to calculate whether a given law will be upheld, or how it will be reinterpreted if challenged in court. Given the current Supreme Court, the words of a statute will be given higher priority compared to various other canons of interpretation, and in general SCOTUS takes seriously any coherent, explicit redefinitions of words as reflecting the will of the legislature. Since "loaded" is explicitly redefined in the New York statute, there is little room to argue. In some other situation, a redefinition might be incoherent in which case the courts would have to decide how the word is to be interpreted (the courts will not reach an absurd conclusion just because the legislature enacted a certain bit of wording).
