'arrhythmy' originates from Greek, specifically the element 'a-' (ἀ-, without) plus 'rhythmḗ' (ῥυθμή, rhythm), where 'a-' meant 'not/without' and 'rhythmḗ' meant 'rhythm'.

'arrhythmy' developed as a variant of the classical Greek-derived medical term 'arrhythmia' (Late Latin/Medieval Latin 'arrhythmia'), entering English in medical use; the shorter form 'arrhythmy' appears as an alternative/dated spelling alongside 'arrhythmia'.

Initially it referred generally to 'absence or disturbance of rhythmic pattern' (from Greek), and it has retained that medical meaning today, typically as 'irregularity of heartbeat' though 'arrhythmia' is now the standard form.