pa

"father," 1680s, from French papa, from Latin papa, originally a reduplicated child's word, similar to Greek pappa (vocative) "o father," pappas "father," pappos "grandfather." The native word is daddy; according to OED the first use of papa was in courtly speech, as a continental affectation, and it was not used by common folk until late 18c.

1814, shortening of grandpappa (1753), childish or familiar form of grandfather (see grand- + pa). Grandpappa is recorded from 1753, grandpop from 1860, grandpappy from 1853.