staple (n.1)

late 13c., stapel, "bent piece of metal with pointed ends," from Old English stapol, stapel "post, pillar, trunk of a tree, steps to a house," from Proto-Germanic *stapulaz "pillar" (source also of Old Norse stopull "tower," Old Saxon stapal "candle, small tub," Old Frisian stapul "scaffold; stem of a tooth," Middle Dutch stappel, stapele "grade, step, basis;" Dutch stapel "a prop, foot-rest, seat," Middle Low German stapel "block for executions," German Stapel "stake, beam").

This formerly was said to be from PIE stebh- (see staff (n.)), but Boutkan points out that Pokorny's entry for that proposed root is made up of "semantically differing material," and gives it no IE etymology, speculating that it is probably a North European substratum word.

A general Germanic word that apparently evolved a specialized meaning in English, though OED finds the connection unclear and suggests the later sense in English might not be the same word.

The meaning "piece of thin wire, bent and formed with two points, driven through papers to hold them together" is attested from 1895.

[principal article grown or made in a country or district] mid-14c., "official market for some class of merchandise, town where certain commodities are taken for sale" (a sense now obsolete), from Anglo-French estaple (14c.), Old French estaple "counter, stall; regulated market, depot."

This is from a Germanic source akin to Middle Low German stapol, Middle Dutch stapel "market," literally "pillar, foundation," from the same source as staple (n.1), the notion perhaps being of market stalls behind pillars of an arcade, or of a raised platform where the king's deputies administered judgment.

The sense of "principal article grown or made in a place" is by 1610s, short for staple ware "wares and goods from a market" (early 15c.) or similar phrases. The extended meaning "principal element or ingredient in anything" is from 1826.

As an adjective, 1610s as "of or pertaining to a market or mart;" hence "chief, principal."

The meaning "fiber of any material used for spinning" is attested from late 15c., but is of uncertain origin and perhaps is a different word.

late 14c., staplen, "fix by means of a large metal clasp," from staple (n.1). It is attested by 1898 as "fix with a wire paper fastener." Stapled is attested late 13c. as "built with pillars." Related: Stapling.