An Etymological Dictionary of Astronomy and Astrophysics

1. A case or occurrence of anything.
   
2. An example put forth in proof or illustration (Dictionary.com).

Etymology (EN): M.E., from O.Fr. instance, from L. instantia “presence; earnestness, urgency,” literally “a standing near,” from instans, → instant.

Etymology (PE): Seté, from set, present stem of setâdan, variant of istâdan “to stand,” → standard, + -é noun suffix.