farewell (a conventional expression used at parting).
noun, plural good-byes.
2.
a farewell.
Also, goodbye.
Origin
1565-75; contraction of God be with ye
Word Origin and History for good-bye
also goodbye, good bye, good-by, 1590s, from godbwye (1570s), itself a contraction of God be with ye (late 14c.), influenced by good day, good evening, etc.