Quoting a dictionary definition of any word is always going to miss the point of a complex ethical dilemma Guy.
Suppose you worked for the Nazi regime during the last war and had access to information on its ‘final solution’ – surely you would say that your duty to humanity takes precedence over your duty to the regime?
You will immediately say no doubt the the Nazi regime was not comparable with the NSA – but that’s also beside the point if you think it through, because once you say ‘it depends on how bad the regime is’ you have already conceded that whistle-blowing corrupt state or corporate practices is justifiable. This is precisely why the legal defense of revelations ’in the public interest’ exists in law, is the foundation of a free press, and is generally regarded as essential to free societies. That the current UK government is seeking to remove this foundation tells you almost everything you need to know about their politics.
To argue that Snowden is a traitor full stop, no debate, is therefore also to argue that it is not in the public interest to know – for example- that big American corporations have been illegally reading their customers’ private correspondence and passing on the information to the CIA, etc.
But in what sense can it not be in my or your interest to know that?