bye-bye
1 of 4interjection
ˈbī-ˌbī 
bī-ˈbī
variants or by-by
—used to express farewell
bye-bye
2 of 4adverb (1)
ˈbī-ˌbī
variants or by-by
: out especially for a walk or ride —used with the verb go
bye-bye
3 of 4noun
ˈbī-ˌbī
variants or by-by
: bed, sleep
lie down … and go to bye-bye
Rudyard Kipling
Rudyard Kiplingbye-bye
4 of 4adverb (2)
ˈbī-ˌbī
variants or by-by
: to bed or sleep —used with the verb go
Word History
Etymology
Interjection
baby-talk reduplication of goodbye
First Known Use
Interjection
circa 1736, in the meaning defined above
Adverb (1)
1917, in the meaning defined above
Noun
1867, in the meaning defined above
Adverb (2)
1909, in the meaning defined above