Which Asian country was formerly known as Siam?

Thailand was formerly known as Siam. The name Siam was used internationally for the Thai kingdom until 1939, when the country officially adopted the name Thailand.

Siam appeared in European records from the early 16th century and became especially associated with the Ayutthaya Kingdom. Its exact origin is debated: proposed roots include Sanskrit śyāma, meaning “dark,” and terms connected with neighboring Mon, Khmer, Chinese, and Tai languages.

The modern name Thailand is commonly interpreted as “Land of the Free,” although scholars also debate the precise history of the word Thai. The country briefly returned to the name Siam after World War II, but Thailand became official again in 1949.

A common mix-up is treating Siam as a former name for all of modern Southeast Asia. It referred specifically to the Thai kingdom, whose borders and political control changed substantially over time.