Peccadillo (noun)

1. A minor or trivial sin or wrongdoing.
2. A slight or minor offence or mistake.

Origin:

From spanish pecadillo ("small sin"), from pecado ("sin") + -illo, means a minor or trivial sin or wrongdoing.

Examples:

1. Lying is not a peccadillo, it's a serious moral failing.
2. His peccadillo of smoking was something he was trying to quit.
3. The peccadillo was a minor crime.
4. The peccadillo was a minor mistake.
5. The peccadillo was a small sin.