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quack [2] 
  n 
1 
a an unqualified person who claims medical knowledge or other skills 
b (as modifier) 
a quack doctor  
2  (Brit., Austral., and N.Z.) 
informal a doctor; physician or surgeon 
  vb 
3 intr to act in the manner of a quack 
  (C17: short for quacksalver) 
 quackish  adj 

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