It's possible you've encountered a typo or misspelling. Perhaps you meant "arhythmic", which is the opposite of rhythmic.
Here's a breakdown:
* Rhythmic: Characterized by rhythm, a regular pattern of sounds or movements. Examples: rhythmic music, rhythmic breathing.
* Arhythmic: Lacking rhythm, irregular or unpredictable. Examples: arrhythmic heartbeat (an irregular heart rhythm), arrhythmic speech (disjointed or non-fluent).
If you're curious about a specific word, please double-check the spelling or provide more context.