lull: [14] There are several words similar to lull in various Germanic languages, including Swedish lulla ‘lull’ and Dutch lullen ‘prattle’, but it is not clear to what extent they are interconnected. But either individually or collectively they all no doubt go back ultimately to a repitition of the syllable lu or la, used in singing a baby to sleep. Lullaby was coined from lull in the 16th century, perhaps using the final syllable of goodbye. [lull etymology, lull origin, 英语词源]