Karel Capek's play 'R.U.R.' introduced what word into the English language?

R.U.R. is a 1920 science fiction play by the Czech writer Karel Čapek. R.U.R. stands for Rossumovi Univerzální Roboti (Rossum’s Universal Robots). However, the English phrase Rossum’s Universal Robots had been used as the subtitle in the Czech original. It premiered on 25 January 1921 and introduced the word "robot" to the English language and to science fiction as a whole.

R.U.R. quickly became famous and was influential early in the history of its publication. By 1923, it had been translated into thirty languages.

The play begins in a factory that makes artificial people, called roboti (robots), from synthetic organic matter. They are not exactly robots by the current definition of the term: they are living flesh and blood creatures rather than machinery and are closer to the modern idea of clones. They may be mistaken for humans and can think for themselves. They seem happy to work for humans at first, but a robot rebellion leads to the extinction of the human race. Čapek later took a different approach to the same theme in War with the Newts, in which non-humans become a servant class in human society.