| paraxial | <microscopy> Referring to the spacing of rays closely surrounding the principal axis of a lens system. See: eyepiece, parfocal. (05 Aug 1998) |
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| paraxial mesoderm | A thickened mass lying at either side of the midline embryonic notochord; on segmentation, it forms the paired somites. (05 Mar 2000) |
| paraxial rays | In geometric optics, those ray's focused at the principal point. (05 Mar 2000) |