on demand

on demand idiom
When needed or asked for, as in She's always ready to sing on demand, or Nowadays infants are generally fed on demand. This usage is a broadening of this phrase's meaning in finance, that is, “payable on being requested or presented,” as in This note is payable on demand. [Late 1600s]

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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