The language one first learned; the language one grew up with; one's native language.
1973, Noel Pitts Gist & ‎Roy Dean Wright , Marginality and Identity , Throughout their long history as a minority, Anglo-Indians learned their "father tongue" but were indifferent to their "mother tongue," an indigenous Indian language.
1993, Janice Rae Williamson , Sounding differences: conversations with seventeen Canadian women writers , A father tongue is a foreign language, therefore English is a foreign language not a mother tongue.
2011, Wendy Doniger , The Implied Spider , Ramanujan has also argued that many Hindu men have both a mother tongue (the everyday language, such as Tamil, spoken by women downstairs, in the back, in the kitchen) and a father tongue (once Sanskrit, more recently English, the literary lingua franca spoken—or at least discussed—by men in the front rooms).
The language spoken by one's mother, when it differs from that spoken by one's father.
2006 , Yo Jackson , Encyclopedia of Multicultural Psychology , Questions about respondents' place of birth, their parents' place of birth, nativity, and language use (called “mother tongue†and “father tongueâ€) were added to the Census between 1850 and 1960.
1854, Henry David Thoreau , Walden, or Life in the Woods , The other is the maturity and experience of that; if that is our mother tongue, this is our father tongue, a reserved and select expression, too significant to be heard by the ear, which we must be born again in order to speak.
1992, Gail B. Griffin , Calling : essays on teaching in the mother tongue , We learn the father tongue to prove we have outgrown the mother tongue.
2017, Andrew Norris , Becoming Who We Are , In each case, we are reborn -- a fact that explains Thoreau's preference here for the father tongue over the mother tongue, as Cavell explains: "A son of man is born of woman; but rebirth, according to our Bible, is the business of the father."