Underhanded (adjective)

1. Dishonest or deceitful.
2. Done in a secret or sneaky way.

Origin:

Early 17th century: from under- + handed.

Examples:

1. The underhanded tactics used by the company were unethical.
2. His underhanded behavior was discovered and he was fired.
3. The underhanded deal was a complete surprise to everyone.
4. She had an underhanded way of getting what she wanted.
5. The underhanded political campaign was filled with lies and deceit.