There Is a Difference Between 'Utmost' and 'Upmost'
by Meghan Moravcik Walbert on Offspring, shared by Me from Lifehacker on (#4WFY5)

I was writing a sentence the other day that included the sentiment that something was of "the utmost importance." And I paused. Was it utmost? Or was it upmost? I was pretty sure it was "utmost," but I was also pretty sure I'd seen/heard "upmost" at some point in my life. What's the difference?