the world > movement > rate of motion > [noun] > decreasing rate of movement or progress > causing > one who or that which (4)
With of. A person who or thing which slows down or delays something.
A person who or thing which holds back, slows down, or delays something, esp. with regard to progress or development. Now rare.
figurative or in figurative context. A retarding influence or agency.
a person who or thing which slows something down.