Does Djervi's name carry an inherited Slavonic sense, or is it a label of a different kind?

Djervi, the twelfth Glagolitic letter, sits well before the point in the alphabet recitation where letter names turn opaque or Greek-derived (that boundary falls at Tvrido, the twenty-first letter). Its own description states its sound, its regional history and its descendant the Serbian djerv, but gives no Slavonic word or sense behind the name itself, and no source consulted states whether this is a settled absence or simply unresearched.