Browsing the internet tonight to check my understanding of the difference between the prefixes hyper and hypo, I've come across an interesting-looking game called MooT.
I was thinking how strange it is that we have taken two similar-sounding prefixes from the Greek language and thus set ourselves up for confusion - hyper meaning above, and hypo, meaning under. I always remember that hypo means "under", because I visualise a hypodermic, which goes under the skin.
The most frequent confusion of these two prefixes, in my experience, is in a school situation, when someone remarks that a child is hypo. I always have a vision of a quiet, sleepy child who is "under the weather", but the speaker means a child who is overactive. The Online Etymology Dictionary says the use of hyper as a stand-alone word to mean overexcited, was first attested in 1942.
I would say that I've heard hypo used much more frequently than hyper, in this context, and I wonder if it will eventually be the preferred word, even though it has the opposite meaning.
A Google search on hypo landed me on the Moot site, and I think the game looks like great fun.