A family or familiar word for a father, roughly equivalent to English words like “daddy” (VT47/10, 26; VT48/19), a simplified form based on the root √AT(AR) (VT48/19).
Conceptual Development: In the Qenya Lexicon of the 1910s the familiar form was ᴱQ. atta, as opposed to the normal form for “father” which was ᴱQ. attu (QL/33), and likewise in the Poetic and Mythological Words of Eldarissa (PME/33). In Early Qenya Word-lists of the 1920s, ᴱQ. atto or tatto was the ordinary word for “father” (PE16/135). In The Etymologies of the 1930s, ᴹQ. atto was a hypocoristic (familiar or pet name) for “father” derived from the root ᴹ√ATA “father” (Ety/ATA). Atto seems to be generally used as a familiar word in later writings, most notably in Tolkien’s notes on Elvish Hands, Fingers and Numerals from the late 1960s (see above).
atto noun "father, daddy" (hypocoristic)(ATA, LR:49), supposedly a word in "actual 'family' use" (VT47:26), also used in children's play for "thumb" and "big toe" (VT47:10, 26, VT48:4, 6). The dual form attat listed in VT48:19 seems to be formed from the alternative form atta, though attat was changed by Tolkien from attot. - Compare atya.