Take a gander at the hypocycloid. You may recognize the shape from the logo of an American football team...
My question is, how do you describe the tip of one such shape in common parlance (in other words, the concave, pointy curve making one-fourth of the example asteroid)?
I know the technical term is "cusp," but in usual literature I take it that cusp means "brim" or "edge," rather than a general concept of "where two curves meet." Further, saying "it looks like a cusp" leaves my imagination staring blankly at nothing (and note that this description must be readable--i.e., I can't just hold my hands in a shape and say "it's like that").
Bonus points for the person who can tell me a word to describe the same shape in 3D (with terms better than an "emaciated cone").