Emily Dickinson Lexicon

DAD, or DAD'DY, n. [W. tad; Ir. taid; Arm. tad; Corn. tad or taz; ancient L. tata; Port. taita; Gypsy, dad, dada; Sans. tada; Hindoo dada; Russ. tiatia; Finn. taat.]

Father; a word used by infants, from whom it is taken. The first articulations of infants or young children are dental or labial; dental, in tad, dad, and labial, in mamma, papa.