Definitions for vest-pocket
Random House Webster's College Dictionary
designed to be carried in or as if in the pocket of a vest:
a vest-pocket dictionary.
contained in a small space; compact:
a vest-pocket park.
Origin of vest-pocket:
Small enough to be carried in a vest pocket or other small container.
She carried a vest-pocket copy of the New Testament in her purse at all times.
By extension, anything smaller than would ordinarily be expected.
Levi's apartment was a vest-pocket Graceland; every inch of wall and shelf space was covered by Elvis memorabilia.
Origin: From vest + pocket, referring to the pockets of a suit vest, which are only sized to hold watches, handkerchiefs, wallets, and similarly small items.