Defining "Greatness"
Greatness is a concept heavily dependent on a person's perspective and biases. Whether someone or something is great or not depends from subjective judgements of the value of one person or thing as compared to another.
The concept can be used to emphasise perceived superiority of a person or thing. In Europe, lauded rulers were given the attribute "the Great" (as in Alfred the Great and Peter the Great); during the Roman era and Middle Ages, meanwhile, the Latin equivalent "Magnus" was used (as in Albertus Magnus and Alexander Magnus).
Various Definitions: The property possessed by something or someone of outstanding importance or eminence; enormousness: unusual largeness in size

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or extent or number ; The state, condition, or quality of being great; as greatness of size, greatness of mind, power, etc; Pride or haughtiness