If you arrive somewhere or do something on the dot, you arrive there or do it at exactly the time that you were supposed to. They appeared on the dot of 9.50 pm as always = punctually
the shorter of the two telegraphic signals used in Morse code mark with a dot; "dot your `i's" make a dot or dots scatter or intersperse like dots or studs; "Hills constellated with lights
A small point or spot, made with a pen or other pointed instrument; a speck, or small mark