The most common and most likely answer to this crossword clue is the 7 letter word SAMURAI
I've seen this crossword clue in The Guardian
S
A
M
U
R
A
I
More clues leading to the result SAMURAI
- Curious, like returning top-class Japanese fighter once
- Curious when taken aback by excellent Japanese warrior
- Military type’s strange aura – “I’m after sex”
- I arm USA criminal, an old swordsman
- Military type knocked back drink when having one-on-one
- Lily as climbing flower? That’s Electric Warrior
- Weird when retiring perfectly fit fighters
- Drive back suspect, like top-class fighter of old
- As a warrior, I sure am upset getting 25 split up
- A warrior – one is a revolutionary besieging ancient city on Sunday
Buddy explains!

The straight part
We know that "an old swordsman" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an old swordsman = samurai.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 SAMURAI mean?
SAMURAI noun- In feudal Japan, a soldier who served a daimyo.