flaw
US /flɑː/
UK /flɑː/

1.
a mark, blemish, or other imperfection which mars a substance or object
:
•
The diamond had a tiny flaw that reduced its value.
•
Check the fabric for any flaws before cutting.
2.
a weakness or shortcoming in a plan, statement, or character
:
•
The only flaw in his argument was a lack of evidence.
•
Pride was his greatest flaw.