History of Ayutthaya - Siampedia

Yama	Heaven which rests entirely on air. [Ref: The Wheel of the Law - Alabaster Henry (1871) - Trubner & Co, London - page 308.]
Yak	Genii Yah, or Yakkhas - A kind of demon, represented in Siamese temples as enormous and horrible, though somewhat human in form. They are not absolutely evil, for Buddha himself passed through the state of Yak, whilst on his transmigrating journey towards perfection. They are often associated with the angels [Kumphan angels], but are more often represented as of evil than of good disposition. [The Weel of the Law - Henry Alabaster (1871) - Trubner & Co, London - page 178.]
Yoht	Traditional Thai unit of length equal to 400 sen or 16 Km.
Yukhanthon	One of the mountains surrounding Mount Meru, the centre of the universe in the Three Worlds cosmic geography. [Ref: Reynolds and Reynolds - page 276-8]
Yumna	River, with lotus; One of the five great rivers. There are five similar figures representing the five great rivers (Maha nathi), whose source is in the Himalayan lake Anodat. They are named Kongkha (Ganges), Yumna, Achirawadi, Saraphum, and Mahi. [Ref: The Wheel of the Law - Alabaster Henry (1871) Trubner & Co, London - page 307.]