concentric

adj. having a common center or axis (of circles, spheres, etc.)

Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric. Concentric objects do not necessarily have the same radius. Concentric cable is a cable type used in TN-C-S earthing systems where the combined neutral and earth core completely surrounds the live core(s). This minimises the risk of completely cutting through the combined neutral and earth without first completely cutting through the live cores.Concentric contraction is a contraction in which there is a shortening of the muscle.
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Adjective
1. having a common center; "concentric rings"
(synonym) concentrical, homocentric
(antonym) eccentric, nonconcentric
(similar) coaxial, coaxal

(n.)
That which has a common center with something else.
  

(a.)
Alt. of Concentrical
  

concentric