blue peter · noun, verb1
The flag, serving as a signal of recall for departure, was used by the British Navy from 1777, and the name “blue peter” had become common by the end of the 18th century. An all-blue flag had earlier seen use for the same purpose by the Dutch East India Company. While “blue” obviously refers to the dominant colour of the flag, the origin of the second part of the term, “peter”, is unknown. Often said to be a corruption of “blue repeater”, there is actually no signal flag that goes by that designation. The use of the flag to spell the letter “P” dates from 1857 and so cannot have played a role in the origin of the term. The whist play, introduced by Lord Henry Bentinck, was named by him after the flag.
Blue Peter · noun2
From blue + Peter, likely in reference to the color of the birds. Attested from the 18th century.
Blue Peter · noun3
See blue peter.
Etymology from Wiktionary, CC BY-SA 4.0.