The most common and most likely answer to this crossword clue is the 6 letter word GLAIVE
I've seen this crossword clue in The Guardian
G
L
A
I
V
E
Buddy explains!

The straight part
We know that "sword" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sword = glaive.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 GLAIVE mean?
GLAIVE noun- A light lance with a long, sharp-pointed head.
- A weapon consisting of a pole with a large blade fixed on the end, the edge of which is on the outside curve.
- A sword, particularly a broadsword.