altitude (idea)

To update Webster 1913's definition of an altitude for a geometric figure (2D or 3D):

1. A perpendicular line segment from a vertex to the plane extension of the opposite face.
2. A perpendicular line segment from a vertex to the line extension of the opposite side.
3. A perpendicular line segment between parallel faces or sides, or between a face and a parallel side.
4. The line extension of such line segment.
5. The length of such line segment.

                     |
                     |
                     |C
                    /|\
                  /  a \
                /    l  \
              /      t   \
            /        i    \
          /          t     \
        /            u      \
      /              d       \
    /                e        \
  /                  |         \
A--------------------+----------B
                     |
                     |