Source : Webster's Revised Unabridged Dictionary (1913)

Yellowhammer \Yel"low*ham`mer\, n. [For yellow-ammer, where
   ammer is fr. AS. amore a kind of bird; akin to G. ammer a
   yellow-hammer, OHG. amero.] (Zo["o]l.)
   (a) A common European finch ({Emberiza citrinella}). The
       color of the male is bright yellow on the breast, neck,
       and sides of the head, with the back yellow and brown,
       and the top of the head and the tail quills blackish.
       Called also {yellow bunting}, {scribbling lark}, and
       {writing lark}. [Written also {yellow-ammer}.]
   (b) The flicker. [Local, U. S.]

Source : WordNet®

yellowhammer
     n 1: large flicker of eastern North America with a red neck and
          yellow undersurface to wings and tail [syn: {yellow-shafted
          flicker}, {Colaptes auratus}]
     2: European bunting the male being bright yellow [syn: {yellow
        bunting}, {Emberiza citrinella}]