An Etymological Dictionary of Astronomy and Astrophysics

1. An act or instance of following a custom, rule, or law.
   

2. A customary practice, rite, or ceremony; a rule governing members of a religious order.
   

3. An act or instance of watching (Merriam-Webster.com).

Etymology (EN): → observe; → -ance.

Etymology (PE): Nepâhdâri, on the model of negâhdâri “preservation, protection,” from nepâhdâr, → observant, + -i.