Definition of semidiameter in English:

semidiameter

Pronunciation: /ˌsemēdīˈamitər//ˌsemˌī-/

noun

Astronomy Geometry
  • Half of a diameter; radius.

    • ‘The moon will, at the full, be totally eclipsed, if its latitude is less than the difference between its own semidiameter, and that of the earth's shadow.’
    • ‘By the semidiameter of a celestial object, is meant the angle which the radius of its apparent circular disc subtends at the eye of the observer.’

Origin

Late Middle English: from late Latin.

Pronunciation:

semidiameter

/ˌsemēdīˈamitər//ˌsemˌī-/