noun Two historical Slavic vowels and their corresponding Cyrillic and Glagolitic letters; the vowels were short (possibly ultrashort), and possibly reduced. They were front jer (ь, Ⱏ) and back jer (ъ, Ⱐ). During the development of Slavic languages in certain positions they underwent weakening and were lost (weak jers), and elsewhere retained (strong jers).