Blue Peter
.A flag with a blue ground and white square in the centre, hoisted as a signal that the ship is about to sail. Peter is a corruption of the French partir (leave or notice of departure). The flag is hoisted to give notice to the town that any person having a money-claim may make it before the ship starts, and that all about to sail are to come on board.
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According to Falconer, it is a corruption of the “blue repeater.”
In whist, it is a “call for trumps”; that is, laying on your partner’s card a higher one than is required.
To hoist the blue Peter. To leave.