This chapter presents an in-depth exploration of word formation in the Thai language, focusing on how morphemes combine to create compound and complex words with distinct meanings. The chapter categorizes word formation into several types, including compound words, complex words, synonymous compounds, reduplicated forms, and Pali-Sanskrit blends. It explains how compound words arise from the fusion of independent morphemes, while complex words involve affixation to a base morpheme. Special attention is given to idiomatic compounds and the nuanced distinctions between true compounds, descriptive phrases, and elliptical constructions. The chapter also examines word order restrictions, continuous pronunciation, and non-syntactic relationships within compounds. Additionally, it analyzes the formation of royal vocabulary, abstract nouns, and professional terms using specific Thai, Pali, and Sanskrit morphemes. By illustrating the cultural, syntactic, and semantic intricacies of word formation, the chapter equips readers with a deeper understanding of how new Thai words are structured and interpreted, enhancing both linguistic knowledge and lexical competence.