gemstone (n.)

"a precious stone" (especially when cut or polished), c. 1300, probably from Old French gemme (12c.), from Latin gemma "precious stone, jewel," originally "bud," from Proto-Italic *gebma- "bud, sprout," from PIE *geb-m- "sprout, bud" (source also of Lithuanian žembėti "to germinate, sprout," Old Church Slavonic prozebnoti "to germinate").

The two competing traditional etymologies trace it either to the root *gembh- "tooth, nail" [Watkins] or *gem- "'to press." De Vaan finds the second "semantically unconvincing" and leans toward the first despite the difficult sense connection.

Of persons, "a rare or excellent example (of something)" from late 13c. Alternative forms iemme, gimme persisted into 14c. and might represent a survival of Old English gimm "precious stone, gem, jewel," also "eye," which was borrowed directly from Latin gemma.

Old English stan, used of common rocks, precious gems, concretions in the body, memorial stones, from Proto-Germanic *stainaz (source also of Old Norse steinn, Danish steen, Old Saxon sten, Old Frisian sten, Dutch steen, Old High German stein, German Stein, Gothic stains), from PIE *stoi-no-, suffixed form of root *stai- "stone," also "to thicken, stiffen" (source also of Sanskrit styayate "curdles, becomes hard;" Avestan stay- "heap;" Greek stear "fat, tallow," stia, stion "pebble;" Old Church Slavonic stena, Russian stiena "wall").

Sense of "testicle" is from late Old English. The British measure of weight (usually equal to 14 pounds) is from late 14c., originally a specific stone. Stone-fruit, one with a pit, is from 1520s. Stone's throw for "a short distance" is attested from 1580s. Stone Age is from 1864. To kill two birds with one stone is first attested 1650s. To leave no stone unturned is from 1540s.