Quiz: Remember the definition of mal de mer?
early 14c., lullen "hush to sleep," probably imitative of lu-lu sound used to lull a child to sleep (cf. Swedish lulla "to hum a lullaby," German lullen "to rock," Sanskrit lolati "moves to and fro," Middle Dutch lollen "to mutter"). Figurative use from 1570s. Related: Lulled; lulling.
1650s as the name of a soothing drink, from lull (v.). Meaning "period of quiet in a storm" is from 1815.