Just now, talking to my boss on the phone, I used expression "in one fell swoop", referring deployment of files from SourceSafe. I am puzzled about what "fell" means. I thought it was related to "swell". I could not have been more wrong:

From http://www.quinion.com/words/qa/qa-fel1.htm
We now never see it outside this fixed phrase (or perhaps only occasionally in poetic use) but once it was a common word in its own right. One of its relatives is still about: felon, which comes from the same Old French source, fel, evil. Originally a felon was a cruel or wicked person; only later did the word evolve to mean a person who commits a serious crime.

That's fitting, especially considering the nature of SourceSafe.