The most common and most likely answer to this crossword clue is the 7 letter word PLEDGES
I've seen this crossword clue in The Daily Telegraph
P
L
E
D
G
E
S
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 = pledges.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 PLEDGES mean?
PLEDGES noun- A solemn promise to do something.
- A security to guarantee payment of a debt.
- A person who has taken a pledge of allegiance to a college fraternity, but is not yet formally approved.
- A drinking toast.
- To make a solemn promise (to do something).
- To deposit something as a security; to pawn.
- To give assurance of friendship by the act of drinking; to drink to one's health.