hacker ˈhakə noun
1. a person who uses computers to gain unauthorized access to data.
2. a person or thing that hacks or cuts roughly.
And only after you expand it, do you get under (1):
> informal an enthusiastic and skilful computer programmer or user
...which isn't exactly it, either. Also, I seem to remember it "google define" used to name the sources, but it doesn't seem to do so for this one.
Wikipedia is right on the money, though [1] [2].
[1] http://en.wikipedia.org/wiki/Hacker
[2] http://en.wikipedia.org/wiki/Hacker_(term)