[dejv]

Robota was involuntary work for feudal lord during middle ages. The class of people required to do such work were called robotnik (in singular).

[danielam]

"Robotnik" is still used in Polish to mean someone who does manual labor and the like. The pejorative "robol" translates as "prole" as in "proletarian".

[dejv]

When Capek created word robot using robotnik as a base, the term was not used for close to 200 years. Czech translation of robotnik in Polish would be delnik.