Whereat Where*at", adv. [1913 Webster] 1. At which; upon which; whereupon; -- used relatively. [1913 Webster]

They vote; whereat his speech he thus renews. --Milton. [1913 Webster]

Whereat he was no less angry and ashamed than desirous to obey Zelmane. --Sir P. Sidney. [1913 Webster]

2. At what; -- used interrogatively; as, whereat are you offended? [1913 Webster]

The Collaborative International Dictionary of English. 2000.