Glagol stands fourth, writes g, and carries the numeral 3 from Greek gamma. Its name is the Slavonic noun for word, speech or utterance, from the verb meaning to speak. In modern Russian the same word has narrowed to a grammatical term and means simply verb, which is a small record of how much technical vocabulary the Slavonic grammatical tradition built out of ordinary speech.
The letterform is the Greek gamma of the uncial books, a plain right angle, and it kept that shape through the manuscript centuries and into the first printed types. The sound it writes is the stop g, and the fricative pronunciation heard in the southern East Slavic area and in much church reading is a later regional development rather than a property of the letter.
In the numeral series it does ordinary work as 3. Where it becomes conspicuous is in the numbering of the Gospels, the psalms and the odes of the canon, where the third of anything carries this letter with a titlo above it.
It survives in every modern Cyrillic alphabet. Its name did not: the modern Russian alphabet calls its letters by invented syllables rather than by words, a reform of the eighteenth and nineteenth centuries that traded a memorable name for a phonetically transparent one and, in the process, ended the possibility of reading the alphabet as a sentence.