biscuit originally meant cooked twice
Good heavens, I never knew that, and I come from a long line of excellent biscuit makers (not that I inherited any of the talent, mind). Here's what Atomica says:
[Middle English bisquit, from Old French biscuit, from Medieval Latin bis coctus : Latin bis, twice + Latin coctus, past participle of coquere, to cook.]
I reckon this accounts also for their def. 4:
pl. biscuit. Clay that has been fired once but not glazed. Also called bisque.
Wow! I'm trying to think of other bis- words...

I had to edit this in: I remembered that a local restaurant here serves what they call "twice-cooked biscuits"; wonder if I oughta tell 'em what a redundancy that is!