Which of the following best defines the term "strengthen"?

The term "strengthen" refers to the act of making something stronger or more powerful. It conveys the idea of enhancing the existing qualities or capabilities of a person, object, or idea. This aligns perfectly with the definition that includes the word "invigorate," suggesting that the process not only makes something stronger but can also add vitality or energy to it.

In various contexts, "strengthen" can apply to physical strength, such as in training or exercise, emotional resilience, such as building confidence, or arguments and ideas, such as making them more compelling and persuasive. Thus, the answer highlights the positive enhancement inherent in the term "strengthen."