'aperiodic' originates from Greek and Medieval/modern formation combining the Greek prefix 'a-' and the element from Greek 'periodikos' (via Latin/French), where 'a-' meant 'not' and 'periodos' meant 'a circuit, recurring cycle'.

'aperiodic' is formed in English from the negative prefix 'a-' + 'periodic' (which comes from Latin/French from Greek 'periodikos', from 'periodos'); the compound formation produced the English adjective 'aperiodic' with the sense 'not periodic'.

Initially formed simply to mean 'not periodic' or 'without periodicity'; over time the word retained that general sense and was extended as a technical term in mathematics, physics and engineering to describe signals, functions, or motions that lack a repeating pattern.