The most common and most likely answer to this crossword clue is the 9 letter word UNDERLINE
I've seen this crossword clue in Financial Times
U
N
D
E
R
L
I
N
E
More clues leading to the result UNDERLINE
- Oppressed by false story about new mark
- Lower job stress
- Foreign articles associated with work cause stress
- Stress caused by row with subordinate
- Inferior, not good, pill for stress
- Stress in the tube?
- Second-in-command, no good against Spain, shows stress
- Lenin rued revolutionary stress
- Legend of row after two European articles
- Stress column must support two foreign articles
Buddy explains!

The straight part
We know that "stress" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stress = underline.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 UNDERLINE mean?
UNDERLINE noun- A line placed underneath a piece of text in order to provide emphasis or to indicate that it should be viewed in italics or (in electronic documents) that it acts as a hyperlink.
- The character _.
- An announcement of a theatrical performance to follow, placed in an advertisement for the current one.
- To draw a line underneath something, especially to add emphasis; to underscore
- To emphasise or stress something
- To influence secretly.
- Passing under a railway line.