I don’t find our Word of the Week, Dad, in English literature before 1600. The earliest use I’m aware of, in literature, appears in Tourneur’s The Atheist’s Tragedy, when a mocking epicure blurts out, “O dead Dad!” My guess is that the word comes into English through Welsh: tad, father. In the novel How Green Was My Valley, grown sons call their patriarch father Dada, which for them was not baby-talk, but rather the affectionate way to address him: cf. Papa. Though the basic word is tad, Welsh alters the beginnings of nouns under many common conditions, so that my Father = fy Nhad, her Father = eu Thad, and your Father = dy Dad. Jesus, in the New Testament, addressing the Father in prayer, begins, O Dad! It’s strange but true, that of the four forms, the “lenited” or softened Dad is probably the most common, given the typical constructions of sentences. Our Father, in case you’re wondering, is ein Tad.
And yet, ultimately, the word does come from baby-talk, as does Mama. These words seem to be universal in human language. That’s not because they all spring from one identical ancient word. It’s rather that it is natural for babies to make certain sounds as they learn to speak. The easiest of all is the m, made by putting the lips together, like a baby at the breast, and exercising the vocal cords. That’s a sound that all languages seem to have, even Hawaiian, with its paucity of consonants (h, k, l, m, n, p, w). If we keep our lips there but block the air passage, suddenly letting go, we make a p sound, or a b if we use the vocal cords. Also easy for the baby to sound is d: da-da-da-da.
So we see in Hebrew, which is wholly unrelated to English and Latin and Greek and Welsh and German, that father is abba (ab, in ancient Hebrew), and mother is emme.
Children are not just receivers of language, but creators of language too; they are remarkably inventive, and many of their inventions “teach” their parents and enter the language for good. We’ll see this phenomenon again.