retard / retarred are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
retard: (verb) cause to move more slowly or operate at a slower rate. (verb) be delayed.
retarred: NA
retard: r·ih·t·AA·r·d
retarred: NA
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)