[1] : The Collaborative International Dictionary of English v.0.48

lallation \lalla"tion\, n. l. lallare to sing lalla, or
   lullaby: cf. f. lallation.
   an imperfect enunciation of the letter r, in which it sounds
   like l.
   1913 webster

[2] : WordNet (r) 2.0

lallation
     n 1: defective articulation of the `l' phoneme or the phoneme `r'
          is pronounced as `l'
     2: gibberish resembling the sounds of a baby syn: babble, babbling
see also:
babble babbling 

Lallation >> L Words
Lallation, definition of term: Lallation
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