[lul.la.by] n, pl -bies [obs. E lulla, interj. used to lull a child (fr. ME) + bye, interj. used to lull a child, fr. ME by] (1588): a soothing refrain; specif: a song to quiet children or lull them to sleep
[2]lullaby vt -bied ; -by.ing (1592): to quiet with or as if with a lullaby