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Synonyms for Scallywag (same or very similar meaning)

WordNet sense 1 (a white Southerner who supported Reconstruction policies after the American Civil War (usually for self-interest)):

WordNet sense 2 (a deceitful and unreliable scoundrel):
knave, rapscallion, rascal, rogue, varlet

WordNet sense 3 (one who is playfully mischievous):
imp, monkey, scamp

From the ODE community, based on WordNetadd/edit