The most common and most likely answer to this crossword clue is the 4 letter word EFFS
I've seen this crossword clue in The Guardian
E
F
F
S
More clues leading to the result EFFS
Buddy explains!

The straight part
We know that "Swears" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swears = effs.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EFFS mean?
EFFS verb- Fuck (the taboo swear word, but not in the sense "to copulate")