early 14c., lullen "to calm or hush to sleep," probably imitative of lu-lu sound used to lull a child to sleep (compare 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; specifically "to quiet (suspicion) so as to delude into a sense of security" is from c. 1600. Related: Lulled; lulling.
