The definition of a darb is slang for an excellent person or thing.
(noun)An example of a darb is a student who receives the grade of A in every class all through the school years.
See darb in Webster's New World College Dictionary
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noun
Origin: prob. contr. < obs. slang darby, ready money, orig., a strict usurer's bond, short for Father Darby's bonds < surname Darby or Derby