* Prescriptive dictionaries aim to show how language *should* be used. These dictionaries will generally not include swear words because they are considered inappropriate or vulgar.
* Descriptive dictionaries aim to document how language is actually used. These dictionaries will often include swear words, along with their definitions, origins, and usage examples. This is because these dictionaries are trying to capture the full spectrum of language, even the parts that are considered taboo.
So, if you're looking for a dictionary that includes swear words, you'll likely find it in a descriptive dictionary. If you're looking for a dictionary that avoids them, you'll want to look for a prescriptive dictionary.