The most common and most likely answer to this crossword clue is the 7 letter word ACUTELY
I've seen this crossword clue in The Daily Telegraph
A
C
U
T
E
L
Y
Buddy explains!

The straight part
We know that "Severely" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case severely = acutely.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 ACUTELY mean?
ACUTELY adverb- In an acute manner