semimajor axis

/S EH1 M AH0 M AH0 JH ER0 AE0 K S AH0 S/
noun
  1. 1

    Half of the major axis of a circle or ellipse.

  2. 2

    Half of the distances between the two branches of a hyperbola.

Source: https://en.wiktionary.org/wiki/semimajor%20axis