Retard (from dictionary.com)
verb (used with object) – to make slow; delay the development or progress of (an action, process, etc.); hinder or impede.
verb (used without object) – to be delayed.
noun – a slowing down, diminution, or hindrance, as in a machine.
Slang: Disparaging. (a) a mentally retarded person. (b) a person who is stupid, obtuse, [...]