Dictionary
John•ny-on-the-spot
Pronunciation: ( jon'ē-on-&thslash;u-spot', -ôn-), [key]—
n. Informal.
a person who is on hand to perform a service, seize an opportunity, deal with an emergency, etc.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.