The Collaborative International Dictionary of English v.0.48:

Ephod \Eph"od\, n. [Heb. '[=e]ph[=o]d, fr. '[=a]phad to put on.]
   (Jew. Antiq.)
   A part of the sacerdotal habit among Jews, being a covering
   for the back and breast, held together on the shoulders by
   two clasps or brooches of onyx stones set in gold, and
   fastened by a girdle of the same stuff as the ephod. The
   ephod for the priests was of plain linen; that for the high
   priest was richly embroidered in colors. The breastplate of
   the high priest was worn upon the ephod in front. --Exodus
   xxviii. 6-12.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Ephod
   something girt, a sacred vestment worn originally by the high
   priest (Ex. 28:4), afterwards by the ordinary priest (1 Sam.
   22:18), and characteristic of his office (1 Sam. 2:18, 28;
   14:3). It was worn by Samuel, and also by David (2 Sam. 6:14).
   It was made of fine linen, and consisted of two pieces, which
   hung from the neck, and covered both the back and front, above
   the tunic and outer garment (Ex. 28:31). That of the high priest
   was embroidered with divers colours. The two pieces were joined
   together over the shoulders (hence in Latin called
   superhumerale) by clasps or buckles of gold or precious stones,
   and fastened round the waist by a "curious girdle of gold, blue,
   purple, and fine twined linen" (28:6-12).

     The breastplate, with the Urim and Thummim, was attached to
   the ephod.