very thing, the
Exactly what is needed or wanted, as in That hat's the very thing to complete the costume. This idiom, which uses very to denote exact identity, was first recorded in 1768.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.