Meltan may be based on a hexagonal nut, and its tail resembles an exposed wire. Its body is based on mercury, a metallic element that is liquid at room temperature. Mercury can also conduct electricity, as well as react with many other metals to form amalgams, which can hold a specific shape far easier than the pure liquid, hence Meltan's body.
Meltan may be a combination of melt, metal, and たん -tan (diminutive Japanese suffix). It may also be derived from tantalum, coltan, or molten
Source: https://bulbapedia.bulbagarden.net/wiki/Meltan_(Pokemon)
Melmetal has similar design aesthetics to its pre-evolution, Meltan. Its head and features are based on hexagonal nuts,[3] and its tail resembles an exposed wire. Its body is based on mercury, a metallic element that is liquid at room temperature. Mercury can also conduct electricity, as well as react with many other metals to form amalgams
Melmetal's Gigantamax form may have been based on the Cyclops
Melmetal may be a combination of melt and metal
Source: https://bulbapedia.bulbagarden.net/wiki/Melmetal_(Pokemon)