With the bar over it, it looks like either an abbreviation or a nomen sacrum. It made me think of the Rohonc word I tentatively read as "Christ":
From there, I started reading about Glagolitic, and I realized that I should probably look at letter frequencies in Old Church Slavonic as it was written in both Glagolitic and and Cyrillic, so I reanalyzed OCS using the Codex Marianus (Glagolitic) and Codex Suprasliensis (Cyrillic).
One of the interesting things about Glagolitic is that some of the forms of these letters resemble the forms of the most common Rohonc letters. But I can only steal 10 minutes away today, so I'll have to get back to that in another post.