What does the word “onion” mean in Latin?

“Onion comes from a Latin word meaning large pearl.” There are 2 theories about its origin:

"The root of the term 'onion' originates from the classical era where it was assigned the Latin name 'unio', meaning oneness or harmony, or a kind of single onion. The French call it onion. Martin Elcort wrote in his book The Hidden Life of Food, 'The word (onion) was formed by adding the onion-shaped letter o to the word union, giving rise to a new spelling 'ounion'. Later, the letter u was discarded to create a new spelling. A union is something indivisible that, if torn apart, is broken in the process, like an onion."

Another hypothesis, however, argues that it has little to do with the term union: "The only Latin word for onion that I have ever seen until now was "caepa" or its counterpart "caepe," however I find that there is also a word "unio, unionis," which may mean a big single pearl OR an onion. (The usual Latin word for pearl was "margarita"). The American Heritage Dictionary, usually a strong source of etymologies, tends to prefer the idea the that edible bulb was called "unio" because, unlike its cousin garlic, it formed in one sphere rather than many cloves. Perhaps a huge pearl was called a "unio" because it shaped like an onion, rather than the other way around.

Since the first use of the term in either sense appears to have happened at the same time (mid-1st century A.D.), I think we can't be sure of that.