Balderdash

I just learned a new word. Before I say what this word is, keep in mind I learned it in one of my graduate physics courses, let's play a weird game of Balderdash and find out what you all think this word could, or should, mean. The word is "fugacity" pronounced "few-gas-ity" or "fu-ga-city." Hopefully these should lead you to the same pronunciation. Try not to cheat and google it. Although I did try and google this word and I had a hard time sifting through all the text to find a good way to discribe it. I want you all to have fun. Don't limit yourselves to potential physics vocabulary. If you were given this word in a game of balderdash, what would you say it means? Love you all.