whereat

Adverb

where=at

CIDE DICTIONARY

whereat, adv.

At which; upon which; whereupon; -- used relatively. [1913 Webster]
"They vote; whereat his speech he thus renews." [1913 Webster]

"Whereat he was no less angry and ashamed than desirous to obey Zelmane." [1913 Webster]
At what; -- used interrogatively; as, whereat are you offended? [1913 Webster]

whereat, conj. archaic 1 at which place or point.
2 for which reason.