The phrase "the mighty deep" is often used to refer to the vast and seemingly endless expanse of the ocean. However, there are several synonyms that can be used to describe this awe-inspiring body of water. Some alternatives to "the mighty deep" include "the vast expanse of the sea," "the infinite blue," "the ocean depths," "the boundless waters," "the fathomless abyss," and "the immeasurable sea." Each of these phrases conjures up a sense of vastness and power, and can be used to add depth and drama to any piece of writing that involves descriptions of the ocean.