Pokoy stands seventeenth, writes p, and carries the numeral 80 from Greek pi. Its name is the Slavonic noun for rest, quiet or repose, the word used in the prayers for the dead and in the liturgical formula asking that a soul be given rest.
The shape is the uncial pi and it has not changed, which makes this one of the letters that most visibly betrays the Greek parentage of the script to anyone who knows the Greek alphabet and not the Slavonic one.
As a numeral it is 80. It also does duty as an abbreviation in the rubrics of service books, where a single letter under a titlo can stand for a whole recurring instruction, on the assumption that a reader using the book already knows what the instruction says.
The name has one further use. Because the letter is shaped like a lintel resting on two posts, the tradition of teaching the alphabet from named letters gave a ready image to hang the sound on, and the primers made heavy use of that kind of visual association. A method of teaching that names letters after words and pictures rather than after their sounds is slower to reach fluent decoding, which is precisely the objection the eighteenth century reformers made when they replaced the names.