John T
Yes, it's there, fourth definition.
Yes, as is " At present sense 4 is found in print chiefly in letters to the editor and other informal prose, not in serious intellectual writing." The implication is that it is used in that context by more uneducated people who think they know what the word means, but are wrong. Or at least that is what I infer from the full text of the page. The correct definition of the word is in example 1. There are enough people using the word wrong to get the fourth definition included, which is unfortunate. I'm sure that MW will eventually include the word pwned, but it will still be a misspelling of the word owned.