What is the definition of “organism”?

"Organ" is a Greek word meaning a tool, instrument, or one of the five senses. "Organize" means to arrange something to function as a tool, instrument or sense organ. "Organism" is the noun form meaning the result of such arrangement.

An organism can be a single living cell, a complex being considered as the sum of its parts, or any group of beings that act together to a common purpose.