The name 'hackney' is an anglicized derivative of French haquenée—a horse of medium size recommended for lady riders. It then went on to become an adjective to "carriage", and ultimately evolved as a double-noun, "hackney carriage". A carriage or automobile for hire. Commonly available.
Hackneyed is an adjective. Used in a derogatory way to describe something unoriginal and oft repeated.
The sermon was full of hackneyed phrases and platitudes.