The Collaborative International Dictionary of English v.0.48:

Thereupon \There`up*on"\, adv.
   1. Upon that or this; thereon. "They shall feed thereupon."
      --Zeph. ii. 7.
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   2. On account, or in consequence, of that; therefore.
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            [He] hopes to find you forward, . . .
            And thereupon he sends you this good news. --Shak.
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   3. Immediately; at once; without delay.
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