What does "southing" mean?

Southing: The time at which the moon, or other heavenly body, passes the meridian of a place.

Additional senses

  1. 2.(Astron.) Distance of any heavenly body south of the equator; south declination; south latitude.
  2. 3.(Surv. & Navigation) Distance southward from any point departure or of reckoning, measured on a meridian; -- opposed to northing.

Sources