At and On

At noun - A highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium.

On is a synonym for at in movement topic. In some cases you can use "On" instead the word "At" as a preposition or an adverb, when it comes to topics like direction, about. popular alternative

On adverb - Toward a point ahead in space or time.

At is a synonym for on in direction topic. You can use "At" instead the word "On" as an adverb or a preposition, if it concerns topics such as ahead of. popular alternative