The most common and most likely answer to this crossword clue is the 7 letter word UNTRUTH
I've seen this crossword clue in The Guardian
U
N
T
R
U
T
H
More clues leading to the result UNTRUTH
- Seek dull job with hospital doing longest possible shift in fabrication
- Country institution sacking husband over woman's falsehood
- Aunt ruthlessly conceals lie
- Relative’s left behind a book of fiction
- Nut going nuts, pity the story
- Hunt ruthlessly admits lie
- Remorse after abandoning initial attempt to catch whopper
- False statement taken out of account ruthlessly
- One minus one? Pity that’s a lie
- You heard books by baseball player are fiction
Buddy explains!

The straight part
We know that "fiction" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fiction = untruth.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 UNTRUTH mean?
UNTRUTH noun- A lie or falsehood.
- The condition of being false; truthlessness.