[interjection bahy-bahy; noun, adverb bahy-bahy]
  1. Baby Talk. sleep.
  1. go bye-bye, Baby Talk.
    1. to leave; depart; go out.
    2. to go to sleep; go to bed.

Origin of bye-bye

1700–10; apparently orig. nursery phrase used to lull a child to sleep, later construed as reduplicative form of bye, short for goodbye Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018