/ Dictionary / Index D diel: Meaning and Definition of Find definitions for: di•el Pronunciation: (dī'ul, dē'-), [key] — adj. Biol. of or pertaining to a 24-hour period, esp. a regular daily cycle, as of the physiology or behavior of an organism. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. die-hard dieldrin Related Content Daily Word Quiz: nonchalant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language