The Collaborative International Dictionary of English v.0.48:

Exon \Ex"on\, n. [NL., from E. Exe (Celt. uisge water) the name
   of a river.]
   A native or inhabitant of Exeter, in England.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Exon \Ex"on\, n. [F. expect an under officer.]
   An officer of the Yeomen of the Guard; an Exempt. [Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

exon
    n 1: sequence of a gene's DNA that transcribes into protein
         structures; "exons are interspersed with introns" [syn:
         exon, coding DNA] [ant: intron, noncoding DNA]

The Jargon File (version 4.4.7, 29 Dec 2003):

Exon
 /eks'on/, excl.

    A generic obscenity that quickly entered wide use on the Internet and
    Usenet after the passage of the Communications Decency Act. From the last
    name of Senator James Exon (Democrat-Nebraska), primary author of the CDA
    . This usage outlasted the CDA itself, which was quashed a little over a
    year later by one of the most acerbic pro-free-speech opinions ever uttered
    by the Supreme Court. The campaign against it was led by an alliance of
    hackers and civil libertarians, and was the first effective political
    mobilization of the hacker culture. Use of Exon's name as an expletive
    outlived the CDA controversy itself.