Vapid, a.
Etymology: [L. vapidus having lost its lire and spirit, vapid; akin to vappa vapid wine, vapor vapor. See Vapor.]
Having lost its life and spirit; dead; spiritless; insipid; flat; dull; unanimated; as, vapid beer; a vapid speech; a vapid state of the blood. A cheap, bloodless reformation, a guiltless liberty, appear flat and vapid to their taste. Burke. -- Vap"id*ly, adv. -- Vap"id*ness, n.
Shades of meaning
Fernald has no entry of its own for vapid; he lists it under vain.
He lists it without comment; the entries above explain its neighbors.