The (planet) Earth often takes its name from the word “earth”. That is true for most languages. But not all. Brown-colored languages form a peculiar group where Earth and earth are quite different. For example Turkic languages, Armenian, Chechen, Hebrew, Abkhaz, Albanian and Irish.
We inherited astronomy from Latin. The symbol, for example, represents the Hermes’ caduceus, also associated with medicine. Romans named the planet after his god Mercurius (Mercury), the messenger of the gods, mediator between the gods and the mortals, and god of commerce (the name comes from Latin merx “merchant”). This was not new: Babylonians called the planet Nabu, also a messenger in their mythology. All these observations were right, the planet is the fastest, it has an orbital speed of 47.4 km/s. Best delivery service in the solar system.
Not all languages use this name. Mercury corresponds to the Greek god Hermes (Ἑρμῆς), thus in Greek, the name is Ermis. Other languages also have local names for the planet like Arabic or Persian Utarid, Hebrew Kokhav khama. Other languages like Armenian or Turkish had also some local names but they are not used anymore. In the case of Lithuanians still they have two names, one for the morning star and one for the evening star as that was the belief in ancient times. At some point, some realized that it was the same one.
Why is it such a polysemic word?
Most of the languages have a word for the planet and one for the chemical element. For example, in Ancient Greek ὑδράργυρος (hydrargyros), meaning “water-silver”: ὑδρ (hydr) + ἄργυρος (argyros). This is why the chemical symbol is Hg. Due to this peculiar property of being silvery and liquid, in the Middle ages, alchemists connected this rare element with the swiftest god. Therefore in some languages (the yellow group), the common name became the same. How did it happen?