Modern English uses "cosmos" to mean the entire physical universe, especially when one wants to suggest its scale and grandeur. The Greek kosmos from which the word descends meant nothing of the kind. It meant simply "order" or "arrangement" — the way one might order a household or arrange flowers in a vase.
Pythagoras Names the Universe
According to ancient sources, the philosopher Pythagoras was the first to apply kosmos to the universe as a whole. His point was philosophical: the universe is not chaotic but ordered, structured by mathematical relationships and harmonies. To call the universe a kosmos was to make a claim about it — that it is, fundamentally, a tidy and intelligible thing. The word stuck.
From Cosmos to Cosmetic
The same Greek word seeded a less grandiose family of English words: cosmetic, cosmetology. Kosmētikos in Greek meant "skilled in arranging" — especially in arranging hair and ornaments. So when you put on cosmetics, you are, etymologically, putting your face in order. The same root that produced "the universe" also produced "lipstick." The Greek instinct to find order beautiful runs through both senses.
Cosmos vs. Universe
"Universe" is the Latin alternative, from universum ("the whole, the all," literally "turned into one"). The two words are near-synonyms in modern English, but they carry slightly different flavours. Universe is the everything-as-totality. Cosmos is the same everything as a structured, ordered system. When astronomers say "cosmology," they mean the study of the universe as a whole; when they say "cosmography," they mean its description in mappable detail. The Greek root insists on shape.