The Collaborative International Dictionary of English v.0.48:

Concentric \Con*cen"tric\, Concentrical \Con*cen"tric*al\, a.
   [F. concentrique. See Concenter.]
   Having a common center, as circles of different size, one
   within another.
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         Concentric circles upon the surface of the water. --Sir
                                                  I. Newton.
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         Concentrical rings like those of an onion. --Arbuthnot.
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The Collaborative International Dictionary of English v.0.48:

Concentric \Con*cen"tric\, n.
   That which has a common center with something else.
   [1913 Webster]

         Its pecular relations to its concentrics. --Coleridge.
   [1913 Webster]