'periodicity' originates from Modern English formation combining the adjective 'periodic' + the suffix '-ity', ultimately from Medieval Latin/Old French and Greek roots; Greek 'periodos' meant 'a going around, circuit'.

'periodicity' developed in English from 'periodic' (from Old French/Medieval Latin forms derived from Greek 'periodos') with the abstract noun suffix '-ity' to form 'periodicity' in modern usage.

Initially it denoted 'the state or quality of being periodic (in the sense of recurring in cycles)', and over time this core meaning has remained, applied broadly in physics, mathematics, chemistry, and general usage.