[af-ter-mahr-kit, ahf-]
  1. the market for replacement parts, accessories, and equipment for the care or enhancement of the original product, especially an automobile, after its sale to the consumer: The company holds a large share in the automotive radio aftermarket.
  2. any additional market created by a product after the primary market: Television is the perfect aftermarket for old movies.
  3. Stock Exchange. secondary market.

Origin of aftermarket

First recorded in 1935–40; after + market Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Word Origin and History for aftermarket

1940, American English, of automobile parts, from after + market.

Online Etymology Dictionary, © 2010 Douglas Harper