Arrhythmic is a word used to describe something that lacks a regular rhythm or beat. Its antonyms are words that express the opposite meaning or convey a sense of regularity or predictability. Some common antonyms for arrhythmic are rhythmic, regular, consistent, pulsating, and steady. These words describe something that has a predictable or steady pattern, whether it be a musical rhythm, a heartbeat, or any other type of regular movement. Other antonyms for arrhythmic could include organized, structured, methodical, and even-paced. Overall, the antonyms for arrhythmic emphasize a sense of order, regularity, and predictability.