Source : Webster's Revised Unabridged Dictionary (1913)

Anonymously \A*non"y*mous*ly\ ([.a]*n[o^]n"[i^]*m[u^]s*l[y^]),
   adv.
   In an anonymous manner; without a name. --Swift.

Source : WordNet®

anonymously
     adv : without giving a name; "she wrote these letters anonymously"