The most common and most likely answer to this crossword clue is the 6 letter word MILDEW
I've seen this crossword clue in The Times
M
I
L
D
E
W
More clues leading to the result MILDEW
- Fungus, note, will, finally, before the day’s up
- Daughter in a race, initially wearing white coat?
- You and I reflected after moderate disease
- Fungal growth, slight on endless sheep
- Slight sound of disgust at parasitic fungus
- Catcall welcomes single Liberal Democrat in white coat
- Must calm partners
- Placid sheep picked up fungal infection
Buddy explains!

The straight part
We know that "Fungus" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fungus = mildew.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 MILDEW mean?
MILDEW noun- A growth of minute powdery or webby fungi, whitish or of different colors, found on various diseased or decaying substances.
- To taint with mildew.
- To become tainted with mildew.