The most common and most likely answer to this crossword clue is the 9 letter word INFLUENZA
I
N
F
L
U
E
N
Z
A
More clues leading to the result INFLUENZA
- Disease that would be passed quickly by mouth when contracted
- Reason to be in bed with nun, if zeal lapses
- Covers of unethical fanzine stirred up widespread complaint
- Respiratory complaint in New Zealand got by adult inhaling pipe
- *Trendy new area has outlet spreading disease
- Wacky fanzine about Leeds United forwards that’s spread virally
- Strange file — a nun catching unknown disease
- Largely eloquent interruption of neo-Nazi contagion
- Fanzine going gaga over leftists’ leader with upper-class complaint
- Hot New Zealand palms exhaust a tenacious bug
Buddy explains!

The straight part
We know that "L/U" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case l/u = influenza.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 INFLUENZA mean?
INFLUENZA noun- An acute contagious disease of the upper airways and lungs, caused by a virus, which rapidly spreads around the world in seasonal epidemics.