Fasika, the Ethiopian name for Easter, begins with this letter, and the spelling is a small piece of evidence. The word comes from the Greek pascha, which comes in turn from the Aramaic and Hebrew term for the Passover. A Greek p arrived in a language that had no p, and it was written with the letter for f, which was the nearest sound available.
That is worth setting beside Pawlos and Petros, where the same language solved the same problem the other way and added a letter. Both strategies are visible in the lexicon, which suggests the borrowings did not all arrive at once or through the same hands. A word taken in early enough, and used often enough to settle, kept the substitution. A proper name that mattered enough to spell exactly got the new sign.
The feast itself is the centre of the Ethiopian year. It follows the fifty-five days of Abiy Tsom and a vigil that runs through the night, and the calculation of its date belongs to the bahre hasab, the computus taught in the church schools. The letter that opens its name is the twenty-fifth of the fidel, and the reason it opens the name rather than a p is a sound change that happened long before there was a Christian in Ethiopia to say it.