The definition for "discretion" may be found in the Code of Virginia at sections 1-200 and 1-201. Of course, you'll have to have passing familiarity with the past thousand years of Virginia's legal history.
Btw, I generally object to the use of modern dictionary definitions in legal application, because they're now based on how people use words in the vernacular press. Prior to the 1950's they were based on literate and academic usage. The problem is that people misuse words in the popular press because they don't make distinctions. Here's an example: the word, "evacuate", is often used to mean moving people out of an area. But they'll say, "five people were evacuated" when they mean "five people were compelled to leave"; when you evacuate a person, that means to give them an enema; when you evacuate a place, that means you remove the people from that place. Such distinctions are important, and all modern dictionaries do is chronicle misuse.
Another example: the brandishing statute uses the phrase, "point, hold, or brandish"; in two recent cases, the Va. Sup. Ct. used dictionary definitions to figure out how to make that phrase fit the facts of the case in order to hold the defendant guilty of brandishing. So now, "brandish" means to "display in an ostentatious or shameful manner". One might say that anyone who is openly carrying a firearm is therefore guilty of brandishing if someone else is willing to testify that their having seen the gun so ostentatiously and shamefully displayed made them "feel fear". Of course, the plain meaning of the statute would prohibit people from using firearms to cause other people to believe they're about to be injured or killed when there's no good reason for doing so. But that's not how it's being "interpreted".
Here's another pet peeve: it is often said, particularly by judges, that Virginia is a common law jurisdiction and the courts are common law courts. But that last bit is not true. A common law court such as the Court of Queen's Bench has plenary jurisdiction; it represents the power of the Queen to make law, suspend the operation of law, and exercise executive powers as well as the performance of judicial acts. In Virginia, we've taken the monarch's powers and split them up six ways in order to protect the people from excesses of power concentration. We've given power over certain subject matter to the United States and split that up between executive, legislative, and judicial branches. And we've retained all others, and split them up the same way. So courts on this side of the pond are not free to make up new law, no matter what they say about it, and their doing so is an act of tyranny, just as the power of the executive to detain and imprison people indefinitely is beyond the scope of the authority granted. The fact that we live in a common law jurisdiction only means that the common law of England, as it existed in 1607, is the law here unless repugnant to the Constitution or positive laws of the Commonwealth. It does not mean that the courts have the power to perform legislative acts.