The Collaborative International Dictionary of English v.0.48:

Hun \Hun\, n. [L. Hunni, also Chunni, and Chuni; cf. AS. H?nas,
   H?ne, OHG. H?ni, G. Hunnen.]
   One of a warlike nomadic people of Northern Asia who, in the
   5th century, under Atilla, invaded and conquered a great part
   of Europe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Hun
    n 1: a member of a nomadic people who invaded Europe in the 4th
         century
    2: offensive term for a person of German descent [syn: Kraut,
       Krauthead, Boche, Jerry, Hun]