/ Dictionary / Index P petitio principii: Meaning and Definition of Find definitions for: pe•ti•ti•o prin•ci•pi•i Pronunciation: (pi-tish'ē-ō" prin-sip'ē-ī" Lat. pe-tē'ti-ō" pring-kip'i-ē"), [key] — Logic. Logic. a fallacy in reasoning resulting from the assumption of that which in the beginning was set forth to be proved; begging the question. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. petitionary petit jury Related Content Daily Word Quiz: careening Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language