I don't like to be caught using words I don't know for certain. I don't mind talking casually, but when I put anything down on paper, I like to be at least mostly correct. So I use the define: function on google a lot. The last four:
We've done a major reboot recently, so I don't have a more complete list, but others I know I've checked include:
mise en place
in media res
Some are just to check the spelling in case Blogger has it wrong, but often it's to make sure I don't use the word in a not quite correct way. I would hate to embarrass myself...