Thing To Do Today: go cancrizans.

You can learn so much from the derivation of words. 

Mind you, quite a lot of what you learn will be wrong.

Take the word cancrizans. It's mostly used, if it's used at all, in the phrase canon cancrizans, of which more below, but of course any mildly educated person will spot that cancrizans is very likely to come from the Latin word cancer, which means crab. They will also know that a canon is an official of the church, so a canon cancrizans must therefore be a...um...a crabby bad-tempered priest? Or one who resists progressive theology by sidling sideways whenever he can?

As a matter of fact the canon in canon cancrizans is nothing to do with churches: it's the sort of canon where the same tune is played twice in an overlapping sort of a way. One part of a canon may be played upside down (the written-down notes are upside down, I mean, not necessarily the player) or a bit higher or lower, or slower or faster than the original tune. Or cancrizans, which is...no, not sideways, but backwards.

Oi! You will say, but a crab doesn't walk backwards!

Ah, yes: but the Mediaeval Latinists who made up the word cancrizans didn't know that, and so to this day to go cancrizans means to move backwards.

Do watch your step, won't you.

Thing To Do With Care Today: go cancrizans. The Latin cancrizāre means to move crabwise. The word goes right back to the Sanskrit karkata, which means crab.