/ Dictionary / Index H half-plane: Meaning and Definition of Find definitions for: half-plane Pronunciation: (haf'plān", häf'-), [key] — n. Math. the part of the plane on one side of a straight line of infinite length in the plane. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. half pint half-pound Related Content Daily Word Quiz: placid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language