1 Duke - the head of a duchy; in the UK, dukes are the most senior nobles. 2  Marquess. 3  Earl. Outside of the English-speaking world, the title is referred to as Count. 4  Viscount. 5  Baron - the most junior of noble titles.
Ethnic Khmer living in Thailand, in Vietnam, and in Laos speak dialects of Khmer that are more or less intelligible to Khmer speakers from Cambodia. Minority languages include Vietnamese, Cham, several dialects of Chinese, and the languages of the various hill tribes.
Khmer and Vietnamese are members of the Mon-Khmer language family. Vietnamese is a tonal language like Thai and Laotian whereas Khmer lacks it. Khmer is used in Thailand as the royal register, being used to address the royal family. A lot of Khmer words are used in the Standard Thai dialect (aka Bangkokian Thai). Vietnamese is not so close to Thai or Laotian.