"father," by 1851, a nursery or provincial abbreviation of dad.
Entries linking to da
dad n.
"a father, papa," recorded from c. 1500, but probably much older, from child's speech, nearly universal and probably prehistoric (compare Welsh tad, Irish daid, Lithuanian tėtė, Sanskrit tatah, Czech tata, Latin tata "father," Greek tata, used by youths to their elders). Compare papa.