Etymology tree Proto-Indo-European *sem- Proto-Indo-European *sēmi Latin sēmi-bor. English semi- Ancient Greek κίρκος (kírkos)bor. Latin circus Proto-Indo-European *-lós Proto-Indo-European *-elós Proto-Italic *-elos Latin -ulus Latin circulus Old French cerclebor. Middle English circle English circle English semicircle From semi- + circle.