means The formation of a word by imitating the natural sound of the thing it names, like buzz, hiss, or clang.

from Straight from Greek: onomatopoiia, a marriage of onoma 'name' and poiein 'to make' — literally 'name-making.' The Greeks, who also gave us 'poet' from that same poiein, saw the coining of a sound-word as a tiny act of creation. It strolled into English through Latin, keeping its tongue-twisting Greek spelling intact, so the word for words-that-sound-like-things is itself the hardest thing on the page to say.