The antonyms for the word "being lenient" can be stringent, strict, rigid, inflexible, tough, harsh, hardline, stern, uncompromising, and unforgiving. Those who are not lenient are strict in their approach and do not compromise on their principles. They have a firm belief system and adhere to it no matter what. They do not sympathize with those who break laws or rules and believe in strict punishment to deter others. Being lenient or strict both have their advantages and disadvantages depending on the situation. However, it is important to strike a balance between the two and approach situations with empathy and understanding while maintaining discipline and authority.