That type of lexicon does not exist in the world today and it a necessity for people who wish to understand the correct definition (Nirukthi) of words been used by Gothama Samana and other Thathāgathas to describe Nibbāna.
All the Thathāgathas use a special vocabulary to explain the true nature of this world, and it is necessary to realize the Nibbāna. This special vocabulary is called Thathāgathavachana. It is a professional vocabulary similar to the way that medical professionals have their special terms in their professional field and the engineers also use a technical vocabulary specific to them. Only the professional of those fields could understand those professional vocabulary identical to their own fields. Likewise, the Thathāgathas also have their own technical/professional vocabulary that they used to describe the path to Nibbāna. It is not comprehensible by normal linguists unless they specialized in the field, in this case those who attain Nibbāna. What has happened today is that normal linguists have interpreted the Nibbāna Dhamma without themselves attaining Nibbāna. This means that they have not become a professional in the field of Nibbāna and therefore their interpretation has become wrong or misinterpreted. That is why the Gothama Samana the Buddha told his disciples to not teach anyone Nibbāna at least until they become Sothapanna (first stage of Nibbāna). Therefore, it is very important that the Nibbāna dhamma teachers or interpreters at least become Sothapanna before they interpret Nibbāna to anyone else. But what has happened is especially like Western writers Rhys Davids and his students have written many English books by interpreting the Nibbāna path according to their own understanding. We could see that they have tried to understand the Nibbāna from Western perspective. They have published lot of wrong books and brought true dhamma manuscripts from Asia to the United Kingdom and kept them in their possession. It has resulted that Nibbāna was lost from world, instead a new mundane religion built on the Western perspective called Buddhism. This new version was created based on prayers, worships, beliefs, and rituals similar to the other religions that believe in a creator god—and it is far from the original.
Gothama Samana the Buddha or none of the other Thathāgathas never spoke Sanskrit or Pāli. The Pāli was found after 8-9 centuries after the Gothama Samana the Buddha’s Parinbbāna, or even may be some thousands of years after, because the chronology of the existence of the Gothama Samana is uncertain yet. Even though the Sanskrit was widely used at that time, the Gothama Samana the Buddha had warned his disciples not to translate his Dhamma to Sanskrit since those type of man-made languages could not able to convey the correct meaning of his teachings. At the Buddha’s time, the word call “Pāli” was using to designate a line or lines of Dhamma texts (pela or peli). Until the 4th Century CE, this word was not used to designate a language. Neither there was such a language call Pāli as today at Gothama Samana Buddha’s time. Even Thitahakaras also has never spoken Pāli, and they also have used Ardha Māghadhi describe their doctrine.
This professional vocabulary identical to the Nibbāna path was made by using by Suddha-Māghadhi Sabdha Sanna. “Suddha” means “the pure”, and the “Māghadhi (Maga + Adhi)” means the “path to go beyond the existence”. This is a phonetic communication interface which contains the natural sound-signs. This is also called the Language of Nature. Dhamma means the law of Nature and only this special language could describe that “Law of Nature”, or the true nature of the world. This communication interface is not a normal mundane language which has letters or scripts. When pronouncing the sound correctly, the meaning goes to the listener’s mind from its pronunciation. Because the meaning is embedded in the sound, a special energy is also embedded into the sound. Therefore, it is very important to pronounce these sounds correctly. This sound based interface is understood by the other beings exists in higher realms to the human also. The first human settlement that came to this planet from the Apassara Brahma realms were using this sound-based interface to communicate. Each sound of this language has been made up by combining few words of the languages that we used today. Therefore, it is impossible to translate the meaning of this Suddha-Māghadhi sounds on a word-by-word basis to any other manmade languages that we use today. It is necessary to use a few words, or few sentences, to describe a definition of a single sound. The closest language for this is “Elu Prakirt” and Gothama Samana has used this Elu Prakirt also in his Dhamma delivering. However, the Elu Prakirt also does not exist today. The present Sinhala is a language been evolved from Elu Prakirt but the present Sinhala that people use nowadays is widely mixed with Sanskrit and Pāli words.
So, we have identified that the main reason for Nibbana to hide from the world is that modern scholars used Pāli and Sanskrit to find the definition for Thathāgathavachana. Two British writers named Robert Caesar Childers and Rhys Davids published a Pāli English dictionary, and thereafter all of the Western writers used that dictionary to interpret Buddha Dhamma. This has led to given a total misinterpretation of Nibbāna path to the world.
There are special abilities one gets to understand this Thathāgathavachana as a result of gaining wisdom by purifying the mind, but this happens after archiving Magga Pala. This ability is called “Artha Dhamma Nirukthi Patibāna Ñāna”.
After understanding the necessity, we have taken steps to regain and develop a “Thathagatha Vocabulary” (Nibbāna Vachana) and also Elu Prakirt language. We have set up a group scholars and academics to undertake this great task and we hope to publish an encyclopedia/professional manual to provide correct definitions for important Thathāgathavachana words soon. This also will be published in English, German, French, Sinhala, Hindi, Thai, and Burmish.