Opposite over adjacent = tangent (from the Latin tangens, "touching". Because a curve is touched most perfectly only by its tangent line).
Arrrgh, MundaCorMeum beat me to it.
Pyramid, from the Greek pyros, "fire". For of the five elements comprising this world, fire is the one which deals the most pain. And of the five Platonic solids, the tetrahedron, likewise, with its sharp and pointy corners, is the one which hurts the most when you step on it... in bare feet.
