Originally Posted By: lanovami
I normally see the word mercurial in the idiom mercurial rise. A mercurial rise is something I never saw as fickle or volatile. However heard of a mercurial fall, even though it seems just as possible with that definition. Either way the definition makes more sense than just a surging mercury in a thermometer I guess. Can't help but wonder if the person who first coined the phrase mercurial rise didn't grasp the meaning of the word.

I have always heard mercurial as related to a situation or personality which was volatile.
Yes, mercurial has a few definitions. I guess every time we use a word that has multiple meanings ( almost all of them) we should opt for a more wordy way of saying it in case some people don't get it.