From the latin ablative prefix "a-" and "rex" (king). A term coined by the 19th century English philosopher Leon Goldbloom to represent a region where no government rule. The term was meant to represent a place where order does exist but without any guiding person or groups.
While the term was meant as a theoretical discussion tool and was not intended to represent any particular ideology, in later years it was accaparated by monocentrists to designate those state-like entities created by them.
It should be noted that many over the years have justly pointed out that what are refered to as arecsies nowaday bears no resemblance to its original meaning.