Natural (non-vulcanized) rubber.
Etymology: From late 1700s; apparently the Quechua word 'kauchuk' became the Spanish 'cauchuc' and then the French 'caoutchouc'.
"In public discussions the word Cautchouc has been objected to, as being difficult to pronounce, and for that reason it should be called 'Rubber.' I have also adopted this name, which is, indeed, its ordinary one."
- Thomas Hancock, "Personal Narrative of the Origin and Progress of the Caoutchouc or India-rubber Manufacture in England"