papa (n.)

c. 1500, colloquial diminutive of dad, with -y (3). Slang daddy-o is attested by 1949, from bop talk.

Daddy-long-legs is from 1814 in Britain as "crane-fly," a slender, long-legged summer fly. In the U.S., it was used by 1865 as the word for a spider-like arachnid with a small round body and very long, slender legs.

A superstition obtains among our cow-boys that if a cow be lost, its whereabouts may be learned by inquiring of the Daddy-Long-legs (Phalangium), which points out the direction of the lost animal with one of its fore legs. [Frank Cowan, "Curious Facts in the History of Insects, Including Spiders and Scorpions," Philadelphia, 1865]

"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.