Olive oil comes from olive, grapeseed oil comes from grape seeds, peanut oil comes from peanuts and canola oil comes from... rapeseed. The plant known as "rape," from a Latin word for "turnip," is a domesticated crop in the widely cultivated Brassicaceae family (also known as the mustard family, the cabbage family, or the cruciferous vegetables). Although the word has disturbing connotations today, during World War II people thought nothing of referring to "rapeseed," and the oil from those seeds was used for industrial purposes.
The real problem with the name "rapeseed oil" is that the oil was so toxic that the FDA banned it for human consumption in 1956. So when Canadian growers bred a new variety of rapeseed in the 1970s with a lower content of the toxic erucic acid, they decided they needed a new name for it.
The term canola was coined from "Canadian oil, low acid" to convince consumers that this oil was safe to eat. And while "canola" was originally a registered trademark, the term became so widely known that the trademark was eventually abandoned, and "canola" became the default term in many countries for any low-erucic rapeseed oil.
