The Collaborative International Dictionary of English v.0.48:

Vapid \Vap"id\ (v[a^]p"[i^]d), a. [L. vapidus having lost its
   life 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.
   [1913 Webster]

         A cheap, bloodless reformation, a guiltless liberty,
         appear flat and vapid to their taste.    --Burke.
   [1913 Webster] -- Vap"id*ly, adv. -- Vap"id*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vapidly
    adv 1: in a vapid manner; "a vapidly smiling salesman"