The most common and most likely answer to this crossword clue is the 12 letter word HIGHLIGHTING
I've seen this crossword clue in The Sunday Telegraph
H
I
G
H
L
I
G
H
T
I
N
G
Buddy explains!
The straight part
We know that "Showing stress" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case showing stress = highlighting.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 HIGHLIGHTING mean?
HIGHLIGHTING verb- To make prominent; emphasize.
- To be a highlight of.
- To mark (important passages of text), e.g. with a fluorescent marker pen or in a wordprocessor, as a means of memory retention or for later reference.
- To dye (part of the hair) a different color than the rest.
- To seek the attention of (a user) on IRC by mentioning their name in a message, causing that message to appear highlighted on their screen.
- The visual emphasis of text by means of a highlight.
- An area of the skin or hair containing highlights.
- Causing emphasis, drawing attention; revealing.