nupassana or upassana?

A Wikipedia article about Sati uses the word "upassanā" > According to Grzegorz Polak, the four upassanā have been misunderstood by the developing Buddhist tradition, ... https://en.wikipedia.org/wiki/Sati_(Buddhism) However, I could not find the word in Pali dictionary and a Google search did not explain the term. The term 'nupassana' however is found on Google but neither in Pali dictionar . There is upasana in Sanskrit. What is this term upassana or nupassana and where is it used?