The word "pacer" is often used to describe a person or thing that sets a certain rhythm or pace. There are several synonyms for this term that can add variety to your writing or speech. One option is "guide," which implies a sense of leadership or instruction in setting the pace. "Leader" is another synonym that emphasizes the idea of someone who leads by example, while "pace-setter" is a more specific term that refers directly to setting a pace. Additional options include "rhythmic controller," "rhythm master," "timekeeper," and "metronome." All of these terms can help you convey the same basic idea in a slightly different way, adding nuance and interest to your language.