Source : Webster's Revised Unabridged Dictionary (1913)

Ignoramus \Ig`no*ra"mus\, n. [L., we are ignorant. See
   {Ignore}.]
   1. (Law) We are ignorant; we ignore; -- being the word
      formerly written on a bill of indictment by a grand jury
      when there was not sufficient evidence to warrant them in
      finding it a true bill. The phrase now used is, ``No
      bill,'' ``No true bill,'' or ``Not found,'' though in some
      jurisdictions ``Ignored'' is still used. --Wharton (Law
      Dict. ). Burn.

   2. (pl. {Ignoramuses}.) A stupid, ignorant person; a vain
      pretender to knowledge; a dunce.

            An ignoramus in place and power.      --South.

Source : WordNet®

ignoramus
     n : an ignorant person [syn: {know nothing}, {uneducated person}]