mother tongue

noun5

1. •
   The language one first learned; the language one grew up with; one's native language.

   • His mother tongue is a relatively conservative dialect of Aramaic.
2. •
   [before a noun] mother tongue
3. •
   The language spoken by one’s ancestors.
4. •
   The language spoken by one's mother, when it differs from that spoken by one's father.

   • Questions about respondents' place of birth, their parents' place of birth, nativity, and language use (called “mother tongue” and “father tongue”) were added to the Census between 1850 and 1960. — 2006
5. •
   Informal speech, as opposed to educated language.

   • We learn the father tongue to prove we have outgrown the mother tongue. — 1992