Boom! Bang! Crash! When a word is formed from the sound that an associated thing makes, call it an example of onomatopoeia.
In Greek, onomatopoeia (on-uh-mah-tuh-PEE-ah) simply means "word-making," but in English it refers to a very specific process of word-making: an attempt to capture the sound of something. Examples of onomatopoeia in English include burble, buzz, slosh, ratatat, and thud. Words created by onomatopoeia can seem totally natural, but they can be surprisingly different from language to language: in Japanese, dogs say wan wan, but in Greek they say gav gav.