Real Dictionary

-on in American English
an inert gas

-on in American English 1
suffix: a suffix used in the names of subatomic particles ( gluon; meson; neutron), quanta (graviton), and other minimal entities or components (cistron; codon; magneton; photon)

-on in American English 2
suffix: a suffix used in the naming of inert gaseous elements

-on in British English
suffix forming nouns: indicating a chemical substance

on
preposition: If someone or something is on a surface or object, the surface or object is immediately below them and is supporting their weight.
preposition: If something is on a surface or object, it is stuck to it or attached to it.

ON in American English
Heliopolis
in a position above, but in contact with and supported by; upon
abbreviation: Old Norse
preposition: so as to be or remain supported by or suspended from

on in British English
in the position or state required for the commencement or sustained continuation, as of a mechanical operation
abbreviation for: Old Norse
noun
preposition: in contact or connection with the surface of; at the upper surface of