Definition of kryptons:
(n) :
(uncountable) The chemical element (symbol Kr) with an atomic number of 36. It is a colourless, odourless noble gas that only reacts with fluorine. It is one of the rarest gases in the Earth's atmosphere.
(n) :
(countable) An atom of this element.
(n) :
(fiction, DC Comics fictional milieu) A fictional planet, the native world of Superman, named after the element krypton.