That which keeps a running count. Also to oppose — the same word for tallying and for standing against.
Old French contour / countouer (a counting table), from Latin computare (to reckon), from com- (together) + putare (to think, reckon); that which keeps a running tally, and by a separate old sense of contra (against), that which opposes.
That which keeps a running count, and by a separate old sense, that which stands against. The same word carries tallying and opposing without either one being the other's origin.