late 14c., from M.L.G. schelf "shelf, set of shelves," or from O.E. cognate scylfe "shelf, ledge, floor," and scylf "peak, pinnacle," from P.Gmc. *skelf-, *skalf- "split," possibly from the notion of a split piece of wood (cf. O.N. skjölf "bench"), from PIE base *(s)kel- "to cut, cleave" (cf. L. sculpere "to carve"). Shelf life first recorded 1927. Phrase on the shelf "out of the way, inactive" is attested from 1575. Continental shelf first attested 1892.
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with on the shelf
Inactive, not employed, as in With mandatory retirement at 65, many useful employees are put on the shelf.
[ Second half of 1500s
In a state of disuse, as in We'll have to put her proposal on the shelf until we have more funds.
[ Late 1800s
Without prospects of marriage. For example, After she broke her third engagement, her parents were sure she'd be on the shelf. This usage is always said of a woman and today considered offensive. It is probably obsolescent.
[ Early 1800s
All these usages allude to an article left on the shelf of a store, bookcase, or the like.