highest in quality
"The greatest piece of art I have ever seen hangs quietly in that small gallery downtown."
superlative form of great: most great
"Among all the athletes who have ever played, Michael Jordan is widely considered the greatest basketball player in history."
In plain English: The greatest is something that is better than anything else.
"He is the greatest player the team has ever had."
Usage: Use "greatest" to describe the person or thing that possesses the highest degree of greatness within a specific group or time period. It functions as a superlative adjective and always requires comparison against others, even if those others are implied.
Derived from Old English grestest, this superlative adjective originates from the root greost meaning "largest" or "most important." It evolved through Middle English to denote the highest degree of quality, size, or extent among a group.