1. Astronomy. the point on the celestial sphere directly beneath a given position or observer and diametrically opposite the zenith.
2. Astrology. the point of a Horoscope opposite the midheaven: the cusp of the fourth house.
3. the lowest point; point of greatest adversity or despair
As I often say, when you hit nadir, the only way to go is up.
The meaning of this one is a bit of a letdown, but I thought it was fun to say...
an agent that promotes the secretion of milk
After my best friend has her baby, I shall make an effort to encourage her to eat many galactagogues to make milk for said baby.