father tongue

noun4

1. •
   A separate language for expressing ideas, as opposed to the vernacular (mother tongue) which is employed for everyday speech.

   • Ironically, it may be argued that in appointing a particular sophisticated form of the vernacular for such use, Dante [Alighieri] was, in effect, creating another ‘father tongue’. — 2013
2. •
   The form of language acquired through education and reading, as opposed to the dialect one grows up speaking; educated or formal language.

   • We learn the father tongue to prove we have outgrown the mother tongue. — 1992
3. •
   The language spoken by one's father, when it differs from that spoken by one's mother.

   • 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
4. •
   A second language that one speaks fluently.

   • Throughout their long history as a minority, Anglo-Indians learned their "father tongue" but were indifferent to their "mother tongue," an indigenous Indian language. — 1973