Which word signifies a significant reduction in intensity or degree?

The correct choice signifies a significant reduction in intensity or degree, and understanding the nuances of the words involved can clarify why "All of the above" is an appropriate answer.

"Diminish" means to decrease in size, extent, or range, which directly relates to a reduction in something's intensity or degree. "Abate" refers to a lessening in severity or intensity, often used in the context of pain or noise, suggesting a decline from a prior state. "Subside" also indicates a reduction, especially in the context of natural phenomena like floods or storms, where conditions gradually return to normal levels.

All three terms convey the concept of reducing intensity or degree, making "All of the above" the most comprehensive and accurate choice. Each word contributes with its particular connotation, but they share the fundamental idea of decrease or reduction. Therefore, the option encompassing all three is the best selection for this question.