The study aims to investigate word classes, functions and contexts of the word /bon/ in Thai, along with its meanings and concepts as well as processes and mechanisms of semantic change and development from Sukhothai period to the reign of King Rama... IX of Rattanakosin period (2016 A.D.), using cognitive semantics, grammaticalization, and lexicalization as conceptual frameworks. There were 2,441 tokens of the word /bon/ in total, according to this study. It was found that, firstly, the word /bon