Source : Webster's Revised Unabridged Dictionary (1913)

Good-by \Good`-by"\, Good-bye \Good`-bye"\, n. or interj. [A
   contraction of God be with ye (God be w[i^] ye, God bw' ye,
   God bwye).]
   Farewell; a form of address used at parting. See the last
   Note under {By}, prep. --Shak.

Source : WordNet®

good-bye
     n : a farewell remark; "they said their good-byes" [syn: {adieu},
          {adios}, {arrivederci}, {auf wiedersehen}, {au revoir},
         {bye}, {bye-bye}, {cheerio}, {good-by}, {goodby}, {goodbye},
          {good day}, {sayonara}, {so long}]