'arrhythmia' originates from Greek, specifically the word 'arrhythmia', where 'a-' meant 'without' and 'rhythmos' meant 'rhythm'.

'arrhythmia' passed from Greek into New/medical Latin as 'arrhythmia' and was then adopted into English with the same form 'arrhythmia'.

Initially, it meant 'lack of rhythm', but over time it evolved into its current meaning of 'an irregularity of (especially the heart's) rhythm'.