Mythonyms are fictional names given to places, objects, or other elements that exist in imagined worlds. These may be toponyms (placenames), fictitious titles, the names of objects, the names of magical or fantastic abilities, or the names of fictional religions, as examples. Any fictional element that is called something possesses a mythonym – the name by which it is referred to within that fictional setting.

Other Atlas often lists example mythonyms for elements to give designers ideas for the types of names they may wish to use.

Worldbuilders introducing mythonyms to an audience should strive to keep the pace of their introduction to an appropriate level. Without knowledge of the world in which they refer to, mythonyms do not make sense. Often worldbuilders will overwhelm audiences with mythonyms and alienate them as mythonyms are in essence a foreign and unknown language.

Providing context clues or a brief description of mythonyms as they are introduced can be helpful in their understanding.