APAD: Pipe Down

Meaning:

   A request to be quiet.

 

Background:

   On sailing ships signals were given to the crew by sounding the boatswain's

   (bo'sun's) pipe. One such was `piping down the hammocks' which was the signal

   to go below decks and retire for the night. When an officer wanted a sailor

   to be dismissed below he would have him `piped down'.

 

   This usage is recorded in Royal Navy workbooks from the 18th century; for

   example, Gillespie's Advice to Commanders & Officers, 1798:

 

     "At four o'clock, P.M. the hammocks should regularly be piped down."

 

   There's no unequivocal link between this naval practice and the `be quiet'

   meaning. It could well have derived from the fact that, if there was a

   disturbance onboard ship, officers could quell it by sending the crew below

   decks, that is, by piping them down. This notion is supported by records of

   ship's crew's being told to `pipe down' rather than signalled to by the use

   of an actual pipe; for example, this report from The Gettysburg Star And

   Banner, April 1850:

 

     `Pipe down!' cried the Captain, and the crew slowly dispersed.

 

- www.phrases.org.uk [edited]

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The NOAD (New Oxford American Dictionary) stresses "imperative"

    pipe down: [often in imperative] Informal Stop talking; be less noisy.

 

but it doesn't have to be. The other day, my son said something about someone

might be better off piping down.

 

AHD (American Heritage Dictionary) says nothing about requesting,

    pipe down: Slang To stop talking; be quiet.

 

It also lists "pipe up" as "to speak up," which might also be used in the

indicative mode.