The smallest mark that can be placed. It has position and no extent, which is why it means a point.
Old English dott, originally the head of a boil or pustule, later narrowed to any small round mark.
Its root is not tidy: dott first named the head of a boil, a small raised mark on skin, long before it settled into any mark on a page. What survived the narrowing is only the smallness and the roundness; the word kept the shape and dropped everything unpleasant about where it started.