/ Dictionary / Index A Arbor Day: Meaning and Definition of Find definitions for: Ar'bor Day" Pronunciation: [key] a day, varying in date but always in the spring, observed in certain states of the U.S. by the planting of trees. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. arbor arboreal Related Content Daily Word Quiz: fidelity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language