The Collaborative International Dictionary of English v.0.48:

Nemesis \Nem"e*sis\ (n[e^]m"[-e]*s[i^]s), prop. n. [L., fr. Gr.
   Ne`mesis, orig., distribution, fr. ne`mein to distribute. See
   Nomad.] (Class. Myth.)
   The goddess of retribution or vengeance; hence, retributive
   justice personified; divine vengeance.
   [1913 Webster]

         This is that ancient doctrine of nemesis who keeps
         watch in the universe, and lets no offense go
         unchastised.                             --Emerson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Nemesis
    n 1: (Greek mythology) the goddess of divine retribution and
         vengeance
    2: something causing misery or death; "the bane of my life"
       [syn: bane, curse, scourge, nemesis]