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.
In July 2017, Universal Music declared Despacito the most-streamed song in history worldwide, surpassing Justin Bieber's Sorry. Universal claimed 4.6 billion views, beating the 4.38 billion for Sorry, but that includes both the original and the remix of Despacito.