The most common and most likely answer to this crossword clue is the 10 letter word UNDERLINED
I've seen this crossword clue in The Guardian
U
N
D
E
R
L
I
N
E
D
More clues leading to the result UNDERLINED
Buddy explains!

The straight part
We know that "Stressed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stressed = underlined.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 UNDERLINED mean?
UNDERLINED verb- To draw a line underneath something, especially to add emphasis; to underscore
- To emphasise or stress something
- To influence secretly.