WHEREAT

whereat. Whereat, ad. at or on which, whereupon

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Where‐at″ (?), adv. 1. 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. 2. At what; — used interrogatively; as, whereat are you offended?