Wat, Vat
sk वास्तु vāstu 'residence', 'reality', 'site', 'essence' | pl vatthu, 'physical base', 'land', 'plot for school-temple' | kh វត្ត vat 'monastery' | th วัด wat 'monastery'.
Wat (or Vat) : temple, pagoda, Khmer Theravada monastery consisting of the religious buildings and the monks' cells.
Vatthu, the Pali origin of the term, both in Khmer and Thai, has a complex Sanskrit etymology, possibly sk वाट vāṭa, 'debate', 'exposition of the truth', 'enclosure', while sk वास्तु vāstu refers to "dwelling", "place fit for the dwelling of gods and humans." In Tantric texts, vastu refers to the “subtle reality”, or "reality conceived by the mind alone."
Angkor Wat, originally dedicated to Vishnu, has since become known as 'the city which is a (Buddhist) monastery'.
Source
ADB research team.