"imperfect pronunciation of the letter -r-, whereby it is made to sound like -l-," as typically among native speakers of Chinese and some other languages, 1864, in form a noun of action from past-participle stem of Latin lallare "sing lullaby," imitative, literally "sing 'la-la.'" Compare Greek lalein "chatter," which also is echoic. The English word was used 1640s in a sense of "childish utterance."