What Does It Mean?

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From our dictionary:
nem•e•sis

(nem'u-sis),
—n.,
—pl.
-ses (-sēz").
1. something that a person cannot conquer, achieve, etc.: The performance test proved to be my nemesis.
2. an opponent or rival whom a person cannot best or overcome.
3. (cap.) Class. Myth.the goddess of divine retribution.
4. an agent or act of retribution or punishment.