means A period is the dot that ends a sentence, or a stretch of time with a beginning and an end (also, the menstrual cycle's monthly arrival).

from From Greek 'periodos,' literally 'a way around' — 'peri-' (around) plus 'hodos' (path or road), the same 'hodos' lurking in 'method' and 'exodus.' It first meant a complete cycle or circuit of time, then narrowed to the punctuation mark that completes the circuit of a sentence. It traveled through Latin 'periodus' and French into English, and the menstrual sense grew from the older 'recurring interval' meaning.