tarras

/T AA1 R AH0 Z/
noun
  1. 1

    A white to grey volcanic tufa, formed of decomposed trachytic cinders, sometimes used as a cement.

  2. 2

    A coarse sort of plaster or mortar, durable in water, and used to line cisterns and other reservoirs of water.

Source: https://en.wiktionary.org/wiki/tarras, https://en.wiktionary.org/wiki/trass