Definition of motherese in US English:

motherese

noun

Psychology Linguistics
  • A simplified form of language used (especially by mothers) in speaking to babies and young children, characterized by repetition, simple sentence structure, limited vocabulary, onomatopoeia, and expressive intonation; child-directed speech; ‘baby talk’.

Origin

1970s; earliest use found in New Scientist. From mother + -ese.

Pronunciation

motherese

/ˌmʌðəˈriːz/