Ancient Seccan is a form of the Seccan language which was used in the times of the Seccan Khanate. Its main differences from the modern language are pronunciation and vocabulary. The two languages also slightly differ in grammar, but it is almost impossible to notice for the common people.
Ancient Seccan has words that are considered lost. It simply means that they are no longer used in the modern language. Most of those words are ranks of the Khanate's nobility and administration. An example of such word is "Noyon". It meant "prince" or "king" and was the title of a local ruler under the Khan. Another lost word is "ondorbuge". It means "high priest" or "high shaman". In the times of the Khanate, the Seccan religion was much more organized than it is today. Ondorbuge was the highest priest in a province. After the fall of the Khanate, the administrative divisions disappeared and it lead to the collapse of the religious organization. However, the words "ondor" - "high", and "buge" - "shaman", are still used today separately.
Today, most Seccans can't read and write. This is a skill unique to the shamans. However, in the past literacy was much more widespread among the Seccans. In the times of the Khanate, they used a syllabic alphabet. It meant that each sign represented a syllable and not a single letter like it is in modern languages. According to scholars, the syllabic alphabet evolved from a pictographic one. Many of the signs show elements that may indicate them symbolizing a word. At some point in Seccan history, the first syllable from each word was taken and became the sound of the appropriate sign.
It is a very old example of Seccan script. It can even predate the Khanate. Look at the signs. They are much more pictographic than the younger examples. I think they are meant to represent words, not syllables