don't swear = don't use any rude words don't swear = don't promise 1- to use rude or offensive language, usually because you are angry: example : Why did you let him swear at you like that? 2- to make a serious promise to do something example He swore revenge on the man who had killed his father. I swear (that) I’ll never leave you.

To swear has two common meanings as in: 1. To swear an oath 2. To use profanity, "foul language" In your case, it´s probably the latter. "Don´t swear in class", meaning don´t say swear words or curse.

don't use dirty words lol

"you don't swear"= you do not use offensive or rude words "Don't swear" = a request not to use offensive language