The Collaborative International Dictionary of English v.0.48:

Fon \Fon\ (f[o^]n), n. [Of Scand. origin; cf. Icel. f[=a]ni
   silly, f[=a]na to act silly, Sw. f[*a]ne fool. Cf. Fond,
   a.]
   A fool; an idiot. [Obs.] --Chaucer.
   [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

FON
       Fiber Optics Network