Currently, when someone says something is chaotic means that it has no order at all: that everything is upside down, jumbled or messy. However, this wasn’t the original meaning Greeks gave to this word.
One of the first writers to mention this term was Hesiod (flourished ca. 700 b.C.) in one of his chief works: The Teogony, where the author talks about the birth of gods and natural personifications. All those creatures actually came out from a huge void or an abyss full of emptiness; a so-called initial gap which separated the two primary elements that later on gave birth to the rest of the elements of the Universe: Earth (Gea) and Heaven (Uranos).
There is a Greek verb that is indeed related to the χάος (chaos) root. Let’s check it out: χαίνω (chaíno) or χάσκω (chásko) means “to open”, “to open one’s mouth”, “to yawn”. Even “to open one’s mouth in order to talk”. Hence the word χάος (chaos) and meaning Hesiodus gave to it as “void gap” from which all the elements of the Cosmos were born. (In fact, the word κόσμος (kósmos) in Greek means “order”, or world in which all things have its own boundaries and can be easily distinguished from one another. This is, in fact, the exact opposite to chaos, where everything is formless and indefinite!)
The Greeks actually used another word to refer to “desorder”, that wasn’t at all related to the word “chaos”, which was ἀταραξία (ataraxía). A term whidely used in philosophy works such as in Epicurus, who described a state of mind that was utterly disordered and thus didn’t allow the person that was under its effects to reach happiness.
The current meaning which we use today as “utter confusion” was first coined from the Ovid Metamorphoses, where Ovid describes chaos as “a raw confused mass, nothing but inert matter, badly combined discordant atoms of things, confused in the one place.” (A. S. Kline’s version). This semantical shift was also extended from the theological use of the word.
Even though, if we take a close look to the first words of the Genesis, we will encounter the same original meaning the Greeks gave to the word chaos: “In the beginning God created the heavens and the earth. Now the earth was formless and empty.”
To sum up, whenever someone says something “is chaotic”, we will have to wonder weather it’s messy or empty!