Rick Renner gives us useful insights into Paul's Greek terminology:
"All serious scholars agree that the language of Ephesians 6:12 is military language. It seems evident that Paul had received a revelation of how Satan’s kingdom has been aligned militarily.
At the very top of Satan’s dark domain, there is a group of demon spirits whom Paul calls “principalities.” The word “principality” is taken from the word archas (arch-as), an old word that is used symbolically to denote “ancient, ancient times.” Furthermore, it is also used to depict individuals who “hold the highest and loftiest position of rank and authority.”
By using the word archas (“principalities”), Paul emphatically tells us that at the very top of Satan’s domain is a group of demon spirits who have held their lofty positions of power and authority since ancient times — probably ever since the fall of Lucifer.
Then Paul continues to mention “powers” as those evil forces that are second in command in Satan’s dark dominion. The word “powers” is taken from the word exousia (ex-ou-sia), and it denotes “delegated authority.”
This tells us that there is a lower-ranking group of demon spirits who have received “delegated authority” from Satan to do whatever they want to do, wherever they desire to do it. This second group of demon spirits have “delegated authority” to carry out all manner of evil and wickedness.
Next, Paul mentions “the rulers of the darkness of this world.” What an amazing word this is! It is taken from the word kosmokrateros (kos-mo-kra-te-ros), and is a compound of the words kosmos and kratos. The word kosmos denotes “order” or “arrangement,” while the word kratos has to do with “raw power.”
When these two words are compounded together into the word kosmokrateros, they depict “raw power that has been harnessed and put into some kind of order.” This word was technically used by the Greek to describe certain aspects of the military.
Why did the ancient Greeks use the word kosmokrateros to depict certain aspects of the military? Because the military was filled with young men who had a lot of natural ability — raw power, if you will. In order for that raw power to be effective, it had to be harnessed and organized (kosmos).
Thus, young soldiers with abounding energy were taught to be submitted, disciplined, ordered and perfectly arranged. This is the picture of rank and file. In the end, all of those men, with all of that raw ability, were turned into a massive force.
Now Paul uses this same idea! By using the phrase “rulers of the darkness of this world,” he tells us that the devil deals with his dark legions of demon spirits like they are troops! He puts them in rank and file, gives them orders and assignments, and then sends them out like troops who are committed to kill....
Finally, Paul mentions “spiritual wickedness in high places.” The word “wickedness” is taken from the word poneros (po-ne-ros), and it is used to depict something that is “bad,” “vile,” “malevolent,” “vicious,” “impious” or “malignant.”
It is important that Paul would save this word until the end of this verse. By saving this phrase until the last, he is telling us the ultimate aim of Satan’s dark domain: these spirits are sent forth from the spirit realm to afflict humanity in a “bad, vile, malevolent, vicious, impious and malignant” way."