1670s, coarse, abusive language of the sort once used by women in the Billingsgate market on the River Thames below London Bridge.

Billingsgate is the market where the fishwomen assemble to purchase fish; and where, in their dealings and disputes they are somewhat apt to leave decency and good manners a little on the left hand. [Grose, "A Classical Dictionary of the Vulgar Tongue," 1788]

The place name is Old English Billingesgate, "gate of (a man called) Billing;" the "gate" probably being a gap in the Roman river wall. The market is from mid-13c.; it was not exclusively a fish market until late 17c.

"principal article grown or made in a country or district," early 15c., "official market for some class of merchandise," from Anglo-French estaple (14c.), Old French estaple "counter, stall; regulated market, depot," 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 else of a raised platform where the king's deputies administered judgment.

The sense of "principal article grown or made in a place" is 1610s, short for staple ware "wares and goods from a market" (early 15c.). Meaning "principle element or ingredient in anything" is from 1826. Meaning "fiber of any material used for spinning" is late 15c., of uncertain origin, and perhaps an unrelated word.

"merchant, vendor," c. 1200, agent noun from sell (v.). Seller's market, in which demand predominates, is recorded by 1934.

"one who drives cattle or sheep to market," early 15c. (late 13c. as a surname), agent noun from drove (n.).