I always took “gank”, mean steal, to be some kind of corruption of gangster.

Just read a game review in which “gank” is said to mean “easily defeat”. Urban dictionary gives the meanings as to kill and to steal, basically, and offers “gang kill” as the origin for the kill meaning.

Can anyone shed light?

It isn’t about killing, it’s about the idea that real gangsters possess the tools, skills, and mindset that allows them to do anything they want to helpless citizens. If you have the same in a game, then you’re the gangster and any manifestation of your superiority towards others is “ganking.”

My 18 year old told me tonight that in his experience with the League of Legends online game the term “gank” means to transition from one type of area, such as a jungle, to another, such as a lane.  Here is a link to a question someone posted in an online forum asking how they can gank effectively in League of Legends.

Edited to fix the link.