Oon means: An archaic British dialectal word for 'oven,' now entirely obsolete. The form 'oon' preserves an older English phonological shape - before the standardization of spelling and pronunciation pushed. The word is mostly archaic or historical; you will only encounter it in old texts, period drama, or school history rather than current teen conversation. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. As a place or proper-name reference it is purely descriptive.