The most common and most likely answer to this crossword clue is the 5 letter word KANJI
K
A
N
J
I
More clues leading to the result KANJI
Buddy explains!

The straight part
We know that "Letters" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case letters = kanji.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 KANJI mean?
KANJI noun- The system of writing Japanese using Chinese characters.
- Any individual Chinese character as used in the Japanese language.