Use "cosmos" generically to refer to the universe as a whole or to outer space. For example, "The cosmos is vast, limitless and filled with strange occurrences."
Use "cosmos" to specifically refer to an ordered, logical notion of the universe. For example, "Science works on the assumption that the universe is cosmos and not chaos."
Use "cosmos" to refer to any self-contained, orderly system with its own set of rules. For example, "Within the cosmos of daytime television, nudity is forbidden."
Use "cosmos" also to name the tall, tropical American herb (Cosmos bipinnatus), planted by gardeners for its colorful pastel blossoms.