What is the term for emotions or reactions that are stable and not easily influenced by external factors?

The term that describes emotions or reactions that are stable and not easily influenced by external factors is "imperturbable." This adjective signifies a state of being calm and unflappable, indicating that a person maintains their composure and does not easily become upset or disturbed by external circumstances. In other words, an imperturbable individual remains steady and unaffected by the ebbs and flows of emotional stimuli around them, embodying a sense of emotional resilience.

The other options do not convey the same meaning. "Mitigate" refers to making something less severe or serious, "maverick" describes someone who is independent-minded and does not conform to established norms, and "monotonous" suggests something that is dull or lacking in variety, all of which do not relate to the concept of stable emotions or reactions.