Quenya 

atto

father, daddy

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.