回答
"space"は元来「空間」という意味で使われますが、「宇宙」という意味で使われるようになったのは、人工衛星の開発などによって宇宙空間が比較的身近な存在として認識されるようになった結果だろうと思われます。
ところで"cosmos"はギリシャ語が語源でピタゴラスが導入したとされているのに対して、"universe"はラテン語が語源であり、共にかなり昔から「宇宙」の意味で使われています。
"cosmos"と"universe"の違いは分かりにくいのですが、"universe"は混沌としたありのままの宇宙を意味するのに対して、"cosmos"は「秩序立った宇宙」という、すべての"universe"を包含するスケールの大きな概念と言えるかと思います。
次のような英文の解説が参考になります:
The words “cosmos” and “universe” are used synonymously as they refer to the same concept which is the world or nature. “Universe” seems to have a narrower or smaller scope than “cosmos,” though, and “cosmos” signifies a larger and more complex system.
Summary:
1.“Cosmos” is a whole harmonious and orderly system that is governed by natural law while “universe” is everything that exists including time and space, matter, and the laws that govern them.
2.The word “cosmos” comes from the Greek word “kosmos” which means “order or orderly arrangement” while the word “universe” comes from the Latin word “universus” which means “whole or entire,” also from the Greek “holos” which also means “whole.”
3.The word “cosmos” was first used by the Greek philosopher and mathematician Pythagoras while the word “universe” was first used by the Roman philosopher, theorist, and statesman Cicero.
4.“Universe” may connote a much smaller scope while “cosmos” implies a larger scope.
http://www.differencebetween.net/science/nature/difference-between-cosmos-and-universe/