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par·ax·i·al (')par-'ak-sē-əl adj relating to or being the space in the immediate neighborhood of the optical axis of a lens or mirror <\paraxial rays>
par·ax·i·al·ly -ē adv
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par·ax·i·al (par-akґse-əl) [para- + axial] situated alongside an axis.Medical dictionary. 2011.