The most common and most likely answer to this crossword clue is the 11 letter word LETTERPRESS
I've seen this crossword clue in The Daily Telegraph
L
E
T
T
E
R
P
R
E
S
S
More clues leading to the result LETTERPRESS
Buddy explains!
The straight part
We know that "Characters showing relief" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case characters showing relief = letterpress.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 LETTERPRESS mean?
LETTERPRESS noun- The printing process in which ink is applied to the top surface of a raised image area, which is then pressed against paper to transfer the image.
- Printing directly from type, in distinction from printing from plates.
- A machine used for such printing.