Meaning of semidiurnal

sem•i•di•ur•nal

Pronunciation: (sem"ē-dī-ûr'nl, sem"ī-), [key]
— adj.
  1. pertaining to, consisting of, or accomplished in half a day.
  2. occurring every 12 hours or twice each day.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.