blue peter: Meaning and Definition of

blue' pe'ter

Pronunciation: [key]
— Naut. Naut.
  1. a blue flag with a white square in the center, designating the letter P in the International Code of Signals, flown by a vessel in port to indicate its imminent departure.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.