History of Thailand
The word Siam may have originated from Pali, Sanskrit श्याम, or Mon ရာမည, with likely the same root as Shan and Ahom. Xianluo was the Chinese name for the Ayutthaya Kingdom, merged from Suphannaphum city-state, centered in modern-day Suphan Buri; and Lavo city-state, centered in modern-day Lop Buri. To the Thai, the name of their country has mostly been Mueang Thai. The country's designation as Siam by Westerners likely came from the Portuguese. Portuguese chronicles noted that Borommatrailokkanat, king of Ayutthaya, sent an expedition to the Malacca Sultanate, at the southern tip of the Malay Peninsula, in 1455. Following their conquest of Malacca in 1511, the Portuguese sent a diplomatic mission to Ayutthaya. A century later, on 15 August 1612, The Globe, an East India Company merchantman bearing a letter from King James I, arrived in "the Road of Syam". Wikipedia