Trig reciprocal function nomenclature? The fact that the reciprocal of $\sin\theta$ is $\csc\theta$, and the reciprocal of $\cos\theta$ is $\sec\theta$ messed with my head for the longest time when I was taking trig. Why are the functions named this way, when an alliterative scheme would seemingly be more sensible?
While I'm at it, what's the reason for choosing the names sine, cosine, and tangent? The words sinusoidal and tangental come to mind, but perhaps these words could have come from the function names, not the other way around.

These two pictures, which I created using xfig in 2008 for this Wikipedia article, may explain the nomenclature.
Vertical lines don't have "co-"; horizontal lines do.


