What's in a name?
土萠 ほたる I refer to her as Hotaru Tomoe, but in Japanese, the order is Tomoe Hotaru. Her family name is Tomoe, which can be broken down into 土 "to," which means "earth," and 萠 "moe," which means "sprouting." This comes from the word for the planet Saturn in Japanese - 土星 "dosei." This might not make very much sense at first - after all, Saturn is not the senshi of the earth, but it might be a reference to the role of Cronus as the deity of agriculture and harvest.
I always found it interesting that Hotaru's surname was so drastically different from all the other senshi's surnames - the inner Senshi have their "___no" (e.g. Aino, Hino, Kino, Mizuno, Tsukino) in direct correspondence with their respective elements. Uranus, Neptune, and Pluto also have their "___oh" (e.g. Tenoh, Kaioh, Meioh) corresponding to the names of their planets. In some ways, then, I guess Hotaru's name has a somewhat similar etymology to that of the other Outer Senshi, but hers is more distinct than the other Outer senshi, with a component not directly derived from the planet name.
Her first name, Hotaru, is written in hiragana (but can be written in kanji as 蛍), and means "firefly." In Japan, spirits of the dead are thought to manifest themselves as fireflies. One example of this can be seen in Final Fantasy X with the similar "pyrefly" concept, where the souls of the departed become balls of light that soar around prettily. (Yeah, that's right, I just alluded to Final Fantasy.) Another is the Studio Ghibli movie (not by Miyazaki!), "Grave of the Fireflies" - a thoroughly depressing but wonderful animated film that deals heavily with death. Hotaru's name is clearly an obvious reference to Saturn's association with death.
It doesn't really get much deeper than that. You can find all this on Wikipedia, but for posterity, I wanted to have it here as well.