The most common and most likely answer to this crossword clue is the 10 letter word GRIEVOUSLY
I've seen this crossword clue in The Times
G
R
I
E
V
O
U
S
L
Y
Buddy explains!
The straight part
We know that "in a severe way" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in a severe way = grievously.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 GRIEVOUSLY mean?
GRIEVOUSLY adverb- In a grievous manner, severely.