The polity now known as Thailand was generally referred to as "Siam" for many centuries. Nationalists renamed it in 1939 in an attempt to be more inclusive of people, particularly in the north, northeast, and south, who had never considered themselves "Siamese" (i.e., indigenous subjects of the state centered on Ayutthaya or Bangkok) but might be persuaded to think of themselves as "Thai." After World War II "Siam" briefly was restored as the country's name in 1946, but little more than a year later "Thailand" became permanent.Laos
The term itself is a neologism, combining the traditional ethnic identity "Thai" with "land" (prathet in Thai). As the word "Thai" also means "free," some people translate the country's name as "Land of the Free," but it is unlikely that that was the original meaning. Many other peoples speaking closely related languages live nearby in Myanmar, China, Laos, and Vietnam; for purposes of convenience, linguists and other scholars sometimes label all of them, along with the Thai, as "Tai" (without the "h").
There is wide variation among systems of transliteration of Thai into the Western alphabet, but in general place-names in this book follow those adopted by the Board on Geographic Names, as used on most published maps.
The word "Laos" was first used by European missionaries and cartographers in the seventeenth century to pluralize the word "Lao," the name of the country's predominant ethnolinguistic group. In the Lao language, which is closely related to Thai, there is no orthographic distinction between plural and singular nouns. In Lao, Laos is known as pathet lao or muang lao, both meaning "Lao country" or "Lao-land," along the lines of prathet thai (Thailand).SOURCE: The Emergence of Modern Southeast Asia: A New History, edited by Norman G. Owen (U. Hawai‘i Press, 2005)
The French used the term "Laos" as the name for their protectorate in the colonial period. After independence in 1954, the country became known as the Kingdom of Laos. In 1975, when the communists came to power and the monarchy was abolished, it was renamed the Lao People's Democratic Republic.