tweedledumand tweedledee

twee·dle·dum and twee·dle·dee (twēd'l-dŭmʹ ən twēd'l-dēʹ) n.

Two people or two groups resembling each other so closely that they are practically indistinguishable.

  [After Tweedledum and Tweedledee, names of two proverbial rival fiddlers, of imitative origin.]

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