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One who is available and ready for action. Thankfully, Pat was Johnny-on-the-spot with buckets when the roof started leaking.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
A person who is available when needed, as in He always is there at the right time, a real Johnny-on-the-spot. [Late 1800s]
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.
A person who is present at a crucial time. This term comes from nineteenth-century America. An early appearance in print is in George Ade’s Artie (1896): “I could see that a Johnny-on-the-spot . . . was trying to keep cases on her.”
The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer