How do things get their names? Ricin is a by-product of the production of castor oil, right? and the Latin term for "castor oil" is ricinus communus. But whence castor oil? seeing as "castor" is part of the Latin name of the humble beaver (Castor canadensis), which has nothing whatever to do with castor oil...or with ricin....How do people determine how a thing gets its name from a Latin derivation?

I mean, like, why ricin? and why castor oil, which derives from the same source and therefore one might think the name would derive from the Latin, too?