ˌsemidiˈameter
[late L. (Boethius): see semi- 7 b.]
The half of a diameter.
| 1551 Recorde Pathw. Knowl. i. Defin., Diameters, whose halfe, I meane from the center to the circumference any waie, is called the semidiameter, or halfe diameter. 1625 N. Carpenter Geogr. Del. i. v. (1635) 117 Astronomers measure the magnitude of the Starres by Diameters and Semi⁓diameters of the Earth. 1648 Wilkins Math. Magick i. vi. 38 That dis-proportion of distance, which there is betwixt the Semidiameter of the Cylinder AB, and the Semidiameter of the rundle with the spokes FA. 1709 Berkeley Th. Vision §44 Fifty or Sixty Semidiameters of the Earth distant from me. 1763 Ann. Reg. 106 A curious halo appeared round the moon. Its semidiameter, from the lower limb of the planet to the opposite arch of the phenomenon, was very near twenty-one degrees and a half. 1816 Playfair Nat. Phil. II. 213, 23659 semidiameters of the Earth, or 93595000 miles. 1885 J. Casey Analyt. Geom. 188 If any tangent meets two conjugate semidiameters of an ellipse. |
| fig. 1614 Jackson Creed iii. xii. 224 By so much doth the Pope..make his authoritie..greater then Christs, which is the semidiameter of this mouth of blasphemies. |
b. Fortif. (See
quot. 1704).
| 1669 Staynred Fortification 1 The Semidiameter of the Outward Polygon. 1704 J. Harris Lex. Techn. I, Semi-diameter..is two-fold, viz. the Greater and Lesser: The former being a Line composed of the Capital, and the Small Semi-diameter of the Polygon: And the other, a Line drawn to the Circumference from the Centre thro' the Gorges. |
Hence
semidiˈametral a., that is a semidiameter.
| 1678 Moxon Mech. Exerc. v. 86 The Semi-Diametral line proceeding from the Center. |