The Collaborative International Dictionary of English v.0.48:

Ew \Ew\ ([=u]), n. [See Yew.]
   A yew. [Obs.] --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

EW
    n 1: military action involving the use of electromagnetic energy
         to determine or exploit or reduce or prevent hostile use of
         the electromagnetic spectrum [syn: electronic warfare,
         EW]