Two clues from yesterday's episode of Jeopardy!. (I meant to post this yesterday, and in fact wrote the post yesterday, but didn't want to give out spoilers, so you're getting it now.)
1. "In math, it's the degree of correctness of a quantity or expression." Answer: "What is accuracy?" (This was in a category which carried the stipulation that every answer had to begin with A and end with Y.)
2. "While writing Principia Mathematica, this twentieth-century British thinker was a lecturer at Cambridge." Answer: "Who is Bertrand Russell?"
My objection to the first one is more that this isn't a mathematical concept; it seems to me that that use of "accuracy" is more common in, say, the experimental sciences.
And to the second one, I believe Russell was the answer given by a contestant and accepted, but Whitehead also might fit this description. (Whitehead left Cambridge just as the first volume of the Principia was published, in 1910.)