mother tongue
noun [ C usually singular ] uk/ˌmʌð.ə ˈtʌŋ/ us/ˌmʌð.ɚ ˈtʌŋ/
B2 母语；本国语；本族语
the first language that you learn when you are a baby, rather than a language learned at school or as an adult
Compare: first languagenative speaker
See also: tongue (LANGUAGE)