Source : Webster's Revised Unabridged Dictionary (1913)

Whereat \Where*at"\, adv.
   1. At which; upon which; whereupon; -- used relatively.

            They vote; whereat his speech he thus renews.
                                                  --Milton.

            Whereat he was no less angry and ashamed than
            desirous to obey Zelmane.             --Sir P.
                                                  Sidney.

   2. At what; -- used interrogatively; as, whereat are you
      offended?

Source : WordNet®

whereat
     adv 1: in consequence of which; "this is a statement whereat the
            listeners may get angry" [syn: {whereupon}]
     2: at or toward which; "we were at a party whereat there was
        lots of dancing"