/ Dictionary / Index P principal argument: Meaning and Definition of Find definitions for: prin'cipal ar'gument Pronunciation: [key] — Math. Math. the radian measure of the argument between −&pgr; and &pgr; of a complex number. Cf.(def. 8c). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. principal principal axis Related Content Daily Word Quiz: philanthropy Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language