vapour: [14] Latin vapor meant ‘steam, heat’. English acquired it via Old French vapour. The now archaic use of the plural, vapours, for a ‘fit of fainting, hysteria, etc’, which dates from the 17th century, was inspired by the notion that exhalations from the stomach and other internal organs affected the brain. Vapid [17] comes from Latin vapidus ‘insipid’, which may have been related to vapor. => vapid
