Cloud once belonged to the rocky landscape. Old English clūd named a rock mass or hill; a resemblance in shape helped carry the word upward into the sky. Its later technical uses extend that history of metaphor still further.
Sources
- Middle English Dictionary · clǒud
Rock and hill senses, with dated examples of the later sky meaning.
- Merriam-Webster · cloud
The word’s etymology and recorded senses.
- Etymonline · cloud
Additional context for the meaning or borrowing history.