unscrupulous
Willing to cheat or lie without caring if it’s wrong.
Unscrupulous means willing to act dishonestly or unfairly to get what you want, without being bothered by guilt or shame. An unscrupulous person ignores rules, ethics, and other people's rights when those things stand in the way of their goals.
Scruples are the moral concerns that make you stop and think “Is this right?” before acting. Someone unscrupulous has cast aside those concerns. An unscrupulous salesperson might lie about a product's quality to make a sale. An unscrupulous politician might spread false rumors about an opponent. An unscrupulous business owner might exploit workers or cheat customers, caring only about profits.
What makes someone unscrupulous is a lack of conscience about their behavior. Everyone makes mistakes, but an unscrupulous person doesn't even wrestle with right and wrong. They see an opportunity to benefit themselves and take it, regardless of who gets hurt.
You might encounter this word in history books describing corrupt officials or dishonest merchants. When someone is called unscrupulous, it's a serious criticism of their character, suggesting they can't be trusted because they place their own advantage above honesty, fairness, and integrity.