"Bad" can mean lousy, or "bad" can mean "good." It's slang, though it seems to be coming into common usage as my generation grows up and passes this usage to our progeny.
"Book" is one, though the multiple meanings aren't contradictory. There are many, many words like this, but the meaning is usually obvious in context.
One of my favorites is "order" which can have different meanings to a thermodynamicist, a waiter, an artist, a lawyer, and a mathematician. And the conflation of meanings caused considerable misunderstanding in the US
I have a mild interest in technical or scientific words that can have different meanings, sometimes in direct conflict, as well as technical words whose meanings are borrowed or corrupted by laypersons.
Example of the first would be the term "closed system" which has multiple, non-equivalent definitions according to different texts. There was another example I discovered during an argument some years ago and involved a dispute over the meaning of the term "natural number" or maybe it was "integer." I can't recall which, but I remember scouring every math book in the company library before finding a very old text that actually agreed with this person whom I (though I was not taking part in the dispute) thought was quite mistaken.
An example of the second might be the use of the words "net" and "web" and "internet" and "usenet" as synonyms. Frankly, most engineers just say that the laypeople are wrong here, while I'm willing to allow that the common understanding of words don't have to be technically correct.
For example, ask most people how to accelerate their car and, besides a stare indicating that you're an idiot for having asked such a stupid question, you would get the quick answer of "step on the gas." Someone who remembered a bit from algebra might note that a deceleration is just a negative acceleration, so stepping on the gas would also accelerate the car. An engineer would include these answers and add that turning the steering wheel while maintaining speed also accelerates the car. Someone trying to be clever might add that one might shift weight in the car, or slam into a wall, or note that they had no car to accelerate, or make some other irritating and seemingly obtuse and irrelevant observation.
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