retardation

The word "retardation" basically means a slowing down or a delay in progress or development. In older medical and school settings, it was also used for intellectual disability, but that use is now outdated and widely offensive. When the word is applied to a person, it usually sounds insulting, even if that was not the speaker's intent.

You may still see it in technical or scientific contexts where it simply means delay or slowing, but in everyday English it carries a strong negative history because of how it was used about people. Today, respectful language uses clearer terms such as "intellectual disability," "developmental delay," or a direct description of a person's specific needs or condition.

"Retardation" fundamentally means a slowing, holding back, or delay in progress or development. In older formal English, it could describe delayed growth, slower movement, or reduced progress in a process, system, or plan. You may still come across related technical uses in science or engineering, where the idea is simply that something is slowed down or delayed.

The word also has an important history in medicine and education. For many years, "mental retardation" was an official term for what is now called "intellectual disability." Over time, that label became strongly associated with mockery, stigma, and disrespect. Because of that history, the word is now widely considered offensive when used about people, even if it appears in older books, records, or laws.

In modern English, the safest and clearest approach is to avoid this word for people altogether. Use terms such as "intellectual disability," "developmental delay," or another specific description that fits the situation. In most everyday contexts, "retardation" sounds harsh and outdated, while in technical contexts it may still keep its neutral sense of delay or slowing. The difference depends heavily on context, but when people are involved, respectful modern wording is the right choice.