Why is the ninth month called September?
c.1200 (but not popular until 1848, as a translation of Humboldt's Kosmos), from Latinized form of Greek kosmos "order, good order, orderly arrangement," a word with several main senses rooted in those notions: The verb kosmein meant generally "to dispose, prepare," but especially "to order and arrange (troops for battle), to set (an army) in array;" also "to establish (a government or regime);" "to deck, adorn, equip, dress" (especially of women). Thus kosmos had an important secondary sense of "ornaments of a woman's dress, decoration" (cf. kosmokomes "dressing the hair") as well as "the universe, the world."
Pythagoras is said to have been the first to apply this word to "the universe," perhaps originally meaning "the starry firmament," but later it was extended to the whole physical world, including the earth. For specific reference to "the world of people," the classical phrase was he oikoumene (ge) "the inhabited (earth)." Septuagint uses both kosmos and oikoumene. Kosmos also was used in Christian religious writing with a sense of "worldly life, this world (as opposed to the afterlife)," but the more frequent word for this was aion, literally "lifetime, age."