The most common and most likely answer to this crossword clue is the 9 letter word GLANDULAR
I've seen this crossword clue in The Guardian
G
L
A
N
D
U
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R
More clues leading to the result GLANDULAR
Buddy explains!

The straight part
We know that "kind of fever" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case kind of fever = glandular.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 GLANDULAR mean?
GLANDULAR adjective- Pertaining to a gland or glands.