[viggity]

It isn't short for debugger. A computer "bug" originated when a small moth (aka bug) was caught in a physical relay on the Mark II. http://en.wikipedia.org/wiki/Software_bug#Etymology

"Debugging" came from the action of trying to find where the bug is at in a program (or, in the original case, the machine)

[bronson]

Quick correction: if you read your link you'll see that glitches have been called bugs since the 1930s or earlier. The Mark II team didn't originate the term but they were very amused to see the literal manifestation.

[andrewaylett]

The note by that moth in the log book says "First actual case of bug being found." Other text on that page reinforces the idea that the word "bug" was in use before that particular bug, not least the quote from Thomas Edison.