In the 21st century the that word is widely understood to be a slur and thus violates rules 1 and 2 on lemmy.ml (where this community is hosted).

Also, you're quoting the definition of the verb, which is typically not applied to people, while the (now deleted, on lemmy.ml at least) grandparent comment was using the word as an adjective... which is.

It’s totally appropriate to use in that context e.g. retarding a fire or the brakes retarding a car, but OPs are clearly not using it like that.