shelf (n.) Look up shelf at
late 14c., from Middle Low German schelf "shelf, set of shelves," or from Old English cognate scylfe, which perhaps meant "shelf, ledge, floor," and scylf "peak, pinnacle," from Proto-Germanic *skelf- "split," possibly from the notion of a split piece of wood (compare Old Norse skjölf "bench"), from PIE root *(s)kel- (1) "to cut, cleave" (see scale (n.1)).

Shelf life first recorded 1927. Phrase on the shelf "out of the way, inactive" is attested from 1570s; of unmarried women with no prospects from 1839. Off the shelf "ready-made" is from 1936. Meaning "ledge of rock" is from 1809, perhaps from or influenced by shelf (n.2). Related: Shelves.
shelf (n.2) Look up shelf at
"sandbank," 1540s, of unknown origin. Related: Shelfy "abounding in sandbanks."