aristocracyyoudaoicibaDictYouDict[aristocracy 词源字典]
aristocracy: [16] Greek áristos meant ‘best’; hence aristocracy signifies, etymologically, ‘rule by the best’ (the suffix -cracy derives ultimately from Greek krátos ‘strength, power’, a relative of English hard). The term aristokratíā was used by Aristotle and Plato in their political writings, denoting ‘government of a state by those best fitted for the task’, and English writers perpetuated the usage when the word was borrowed from French aristocratie: Thomas Hobbes, for instance, wrote ‘Aristocracy is that, wherein the highest magistrate is chosen out of those that have had the best education’, Art of Rhetoric 1679.

But from the first the term was also used in English for ‘rule by a privileged class’, and by the mid 17th century this had begun to pass into ‘the privileged class’ itself, ‘the nobility’. The derived aristocrat appeared at the end of the 18th century; it was a direct borrowing of French aristocrate, a coinage inspired by the French Revolution.
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aristocracy (n.)youdaoicibaDictYouDict
1560s, from Middle French aristocracie (Modern French aristocratie), from Late Latin aristocratia, from Greek aristokratia "government or rule of the best," from aristos "best" (originally "most fitting," from PIE *ar-isto-, superlative form of *ar- "to fit together;" see arm (n.1)) + kratos "rule, power" (see -cracy).

At first in a literal sense of "government by those who are the best citizens;" meaning "rule by a privileged class" (best-born or best-favored by fortune) is from 1570s and became paramount 17c. Hence, the meaning "patrician order" (1650s). In early use contrasted with monarchy; after French and American revolutions, with democracy.