ERN is a 3 letter word that starts with E.

1. \Ern\, Erne \Erne\, n. [AS. earn eagle; akin to D. arend,
   OHG. aro, G. aar, Icel., Sw., & Dan. ["o]rn, Goth. ara, and
   to Gr. ? bird. ???. Cf. {Ornithology}.] (Zo["o]l.)
   A sea eagle, esp. the European white-tailed sea eagle
   ({Hali[ae]etus albicilla}).
   
   

2. \Ern\, v. i. [Cf. {Erme}.]
   To stir with strong emotion; to grieve; to mourn.
   
   Note: [Corrupted into yearn in modern editions of
         Shakespeare.] [Obs.]