:sidecar: n. 1. Syn. {slap on the side}. Esp. used of add-ons
for the late and unlamented IBM PCjr. 2. The IBM PC compatibility
box that could be bolted onto the side of an Amiga. Designed and
produced by Commodore, it broke all of the company's own design
rules. If it worked with any other peripherals, it was by
{magic}.
-- The AI Hackers Dictionary