mid-15c., "box, case," from Old French tronc "alms box in a church," also "trunk of a tree, trunk of the human body, wooden block" (12c.), from Latin truncus "trunk of a tree, trunk of the body," of uncertain origin, probably originally "mutilated, cut off," and perhaps from PIE root *tere- (2) "cross over, pass through, overcome."
The meaning "box, case" is likely to be from the notion of the body as the "case" of the organs. English acquired the "main stem of a tree" and "torso of the body" senses from Old French in late 15c. The sense of "luggage compartment of a motor vehicle" is from 1930. Railroad trunk line is attested from 1843; telephone version is from 1889.
"short, thick stick of wood used for fuel," mid-15c., from Old French billette, diminutive of bille "stick of wood," from Medieval Latin billia "tree, trunk," which is possibly from Gaulish (compare Irish bile "tree trunk").
"either of two round projections of a cannon," 1620s, from French trognon "core of fruit, stump, tree trunk," from Old French troignon (14c.), probably from Latin truncus (see trunk (n.1)).
Old English stocc "stump, post, stake, tree trunk, log," also "pillory" (usually plural, stocks), from Proto-Germanic *stauk- "tree trunk" (source also of Old Norse stokkr "block of wood, trunk of a tree," Old Saxon, Old Frisian stok, Middle Dutch stoc "tree trunk, stump," Dutch stok "stick, cane," Old High German stoc "tree trunk, stick," German Stock "stick, cane;" also Dutch stuk, German Stück "piece"), from an extended form of PIE root *(s)teu- (1) "to push, stick, knock, beat" (see steep (adj.)).
Meaning "ancestry, family" (late 14c.) is a figurative use of the "tree trunk" sense (as in family tree). This is also the root of the meaning "heavy part of a tool," and "part of a rifle held against the shoulder" (1540s). Meaning "person as dull and senseless as a block or log" is from c. 1300; hence "a dull recipient of action or notice" (1540s).
Meaning "framework on which a boat was constructed" (early 15c.) led to figurative phrase on stocks "planned and commenced" (1660s). Taking stock "making an inventory" is attested from 1736. Stock, lock, and barrel "the whole of a thing" is recorded from 1817. Stock-still (late 15c.) is literally "as still as a tree trunk."
late 15c., from Latin truncatus "cut off," past participle of truncare "to maim, mutilate, cut off," from truncus "maimed, mutilated," also "trunk of a tree, trunk of the body," of uncertain origin, probably originally "mutilated, cut off," and perhaps from PIE root *tere- (2) "cross over, pass through, overcome." Related: Truncated; truncating.