stock (n.1)

Middle English stok, from Old English stocc "stump, wooden post, stake; trunk of a living tree; 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").

This is said to be from an extended form of PIE root *(s)teu- (1) "to push, stick, knock, beat" (see steep (adj.)), but Boutkan considers that instead it is "probably" from an extended form of the root *sta- "to stand, make or be firm."

In old use often paired alliteratively with stone (n.). With specific technical senses based on the idea of "principal supporting part" of a tool or weapon (to which others were affixed), such as "block from which a bell is hung," "gun carriage" (both late 15c.).

The sense of "part of a rifle held against the shoulder" is from 1540s. Stock, lock, and barrel "the whole of a thing" is recorded from 1817.

The meaning "line of descent, ancestry" is from late 12c.; that of "original progenitor of a family" is late 14c.; figurative uses of the "trunk of a living tree" sense (compare the notion in family tree and the family sense of stem (n.)). 

In comparisons, the meaning "person as dull and senseless as a block or log" is from c. 1300; hence "a dull recipient of action or notice" (1510s), as in laughing-stock and compare butt (n.3).

early 15c., "supply for future use; collective wealth;" mid-15c., "sum of money set aside for a specific purpose;" Middle English developments of stock (n.1), but the ultimate sense connection is uncertain. Perhaps the notion is of the "trunk" from which gains are an outgrowth, or from stock (n.1) in obsolete sense of "money-box" (c. 1400). Probably several different lines of development are represented here.

The meaning "subscribed capital of a corporation" is from 1610s. The figurative phrase take stock in "repose confidence in, regard as important" is from 1870, from the notion of investment.

In stock "in the possession of a trader" is from 1610s. The meaning "broth made by boiling meat" is from 1764. As "raw material from which anything is made," 1873, especially in reference to paper.

Theatrical use, in reference to a company regularly acting together at a given theater, performing recurring types, or staging a fixed set of plays, is attested from 1708, from the notion of something habitually produced or used. 

Taking stock "making an inventory" is attested from 1736. One's stock in trade in a literal sense was "goods kept on hand by a dealer or storekeeper" (1760s) with figurative use by 1784.

As the collective term for the movable property of a farm, especially horses, cattle, sheep, and other useful animals, it is recorded from 1510s; hence livestock, stockyard. "The application to cattle is primarily a specific use of the sense 'store', but the notion of 'race' or 'breed' ... has had some share in its development" [OED].

"supply (a store) with stock," 1620s, from stock (n.2). The meaning "lay up in store" is from c. 1700. The earliest sense is "imprison or punish (someone) in a restraining device" (stokken, early 14c.). Related: Stocked; stocking.

in reference to conversation, literature, "recurring, commonplace" (as in stock phrase), 1738, a figurative use from the sense of "kept in store for constant use" (1620s), from stock (n.2) "supply for future use."