I. interjection
or by-by ˈbī-ˌbī, bī-ˈbī
Etymology: baby-talk reduplication of goodbye
Date: circa 1736
— used to express farewell
II. adverb
or by-by ˈbī-ˌbī
Date: 1917
: out especially for a walk or ride — used with the verb go
III. noun
or by-by ˈbī-ˌbī
Date: 1867
: bed , sleep
lie down…and go to bye-bye — Rudyard Kipling
IV. adverb
or by-by ˈbī-ˌbī
Date: 1920
: to bed or sleep — used with the verb go