The usual Old English word for cloud was weolcan. In Middle English, skie also originally meant cloud. The four fundamental types of cloud classification (cirrus, cumulus, stratus, nimbus) were proposed by British amateur meteorologist Luke Howard (1772-1864) in 1802. Figuratively, as something that casts a shadow, from early 15c.; hence under a cloud (c.1500).
Thanks for the A2A. Okay, the most famous song in the world is no doubt 'Happy Birthday', followed by various Christmas carols (since the majority of human population is Christian indeed and since Santa is a really famous guy), folk songs, army marches and national anthems.
Now, the Birthday Song finally belongs to the public and is considered one of the most popular songs in the world. It has been translated into many languages, including Mandarin Chinese. It's an easy song to learn in Chinese since it is essentially just two phrases repeated over and over again.