Without letup means high intensity or continuous activity without any breaks. There are various synonyms that can be used for this term, including non-stop, uninterrupted, incessant, relentless, constant, and persistent. These words can be used in different contexts, ranging from work to leisure activities. For example, a factory may run non-stop throughout the day to meet production targets, or an athlete may train incessantly to develop their skills. Similarly, a person may go on a relentless pursuit to achieve their goals, or a dance party may have constant music playing to keep the attendees engaged. In summary, without letup is a term that describes continuous activity, and it has various synonyms that can be used to convey a similar meaning.