gallstone (n.)

"bile, liver secretion," Old English galla (Anglian), gealla (West Saxon) "gall, bile," from Proto-Germanic *gallon "bile" (source also of Old Norse gall "gall, bile; sour drink," Old Saxon galle, Old High German galla, German Galle), from PIE root *ghel- (2) "to shine," with derivatives denoting "green, yellow," and thus "bile, gall." Informal sense of "impudence, boldness" first recorded American English 1882; but meaning "embittered spirit, rancor" is from c. 1200, from the old medicine theory of humors.

"discrete piece of rock," especially not a large one, Old English stan, which was 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).

This is reconstructed to be 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").

From late 12c. as "substance of which stones consist, rock, stone as a medium." The sense of "testicle" was in late Old English. The British measure of weight (usually equal to 14 pounds) is from late 14c., originally a specific stone.

Stone-fruit, "drupe, fruit with a hard stone or nut at the center," is from 1520s. Stone's throw for "a short distance" is attested from 1580s; stone's cast in the same sense is from late 13c., also "a short time." Stone age, "period of human cultural development marked by tools or weapons made of stone," is from 1864; adjectival extended sense of "outmoded, unsophisticated" is by 1927.

To kill two birds with one stone "accomplish two purposes with one act" is attested by 1650s. To leave no stone unturned "use every possible expedient" is from 1540s. To have a heart of stone figuratively is by late 14c.