Q. In some prayers for particular people, the name of the person is given as “P the son (or daughter) of P”. What does the “P” denote?
A. The “P” is short for p’loni, “a certain person”. The root is peleh, “a wonder”. God is called oseh feleh, “He who does wondrous things” (Ex. 15:11). From this root comes a verb that means “to be distinct”, as in Ex. 33:16 (v’niflinu). Eventually there arises a word p’loni which means “such and such”, as in I Sam. 21:3, m’kom p’loni, “such and such a place” (cf. II Kings 6:8), or “so and so”, sometimes linked with almoni, presumably because of the rhyme.
In the Book of Ruth, Boaz calls to a kinsman, “Sit here p’loni almoni, i.e. such and such a person” (Ruth 4:1). Boaz would have known his kinsman’s name (it might have been Tov: see Ruth 3:13), but the text suppressed it, in the view of the rabbis, because the kinsman was reluctant to do a mitzvah.
Louis Finkelstein suggested that sometimes when rabbinic literature used the word p’loni they were hinting at the name of Philo, the Hellenistic philosopher, whose views they knew but did not approve. The notion that Philo can be read into rabbinic material is, however, not very likely.