There are several synonyms for the term "giant sea swells," which can all be used to describe powerful waves. One alternative term is "rogue waves," which refer to unusually large and unpredictable waves that are capable of causing significant damage to ships and structures. Another synonym is "monstrous waves," which denotes waves that are particularly impressive or intimidating in size. "Massive swells" is another suitable alternative, emphasizing the substantial size of the waves. "Huge rollers" is yet another option, with "roller" specifically referring to a wave that moves forward while maintaining its shape. Overall, there are many words that can be used to describe giant sea swells, and choosing the right one may depend on the context and specific connotations of each term.