If we're throwing out random nitpicks, then I would vote for "number?" as the test function name, with "number" or "num" being the coercing function. I think the SICP style of appending a question mark at the end of boolean functions makes for very readable code, and keeps with the Arc design goal of brevity. I do not like "anum" or "anumber", because I think "a____" should in general be reserved for anaphoric macros, for consistency's sake.
