The most common and most likely answer to this crossword clue is the 4 letter word FLAW
I've seen this crossword clue in The Guardian
F
L
A
W
More clues leading to the result FLAW
- Following legislation is a mistake
- Key legislation's defect
- Crack in ground, we're told
- Thief following what you’d think she'd break
- Note wall unfinished, performing U-turn; it’s a weakness
- By the sound of it, puzzle 5 across
- Broadcast story of 8’s mistake
- Weakness
- Defect following piece of legislation
- Crack in ground, by the sound of it?
Buddy explains!

The straight part
We know that "5 across" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case 5 across = flaw.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 FLAW mean?
FLAW noun- A flake, fragment, or shiver.
- A thin cake, as of ice.
- A crack or breach, a gap or fissure; a defect of continuity or cohesion.
- A defect, fault, or imperfection, especially one that is hidden.
- To add a flaw to, to make imperfect or defective.
- To become imperfect or defective; to crack or break.
- A sudden burst or gust of wind of short duration; windflaw.
- A storm of short duration.
- A sudden burst of noise and disorder