retard

To retard something is to slow it down. A lack of fresh fruit and vegetables can retard the growth of a young child.

This word should be used with a lot of caution. Using this word to describe a person is considered offensive and should be avoided. It is often a harmless word when used as a verb. While skiing, a heavy, bulky jacket could retard your progress down the mountain. Keeping a plant out of sunlight would retard its growth.