The word "cement " is not derived from english language. It was derived from the roman langauge.
The meaning of cement in roman was concrete.
There is no clear idea when cement was found as it was used from long ages. Earlier only burnt lime and clay was used in construction. But in the year 1824, joseph aspidin, a british mason who burned lime with alumina found that the resulting material colour appears like colour of rocks/stones available in a place called portland in england. So he kept the name Portland cement.
So only cement is called Portland cement.
Similarly, if cement was mixed with ash/flyash/volcanic ash, it becomes and remains harder if used under the water surface like dams, bridges across rivers etc., This method was adopted even in earlier ages. People mixes this burnt lime and clay with volcanic ashes earlier. This volcanic ashes were earlier available in a place called pozzuoli in Ialy. Also the latin name for volcanic ash was pulvis puteolanus.
So ash mixed cement is called Pozzollana cement or Portland pozzollana cement
