Latin language

The dot over a lowercase i and j has a name: the tittle, from Latin titulus, "heading." In 11th-century Europe, dense Gothic script made letters into rows of identical strokes, so scribes marked i and j to tell them apart. It later shrank to today's small dot.

AM stands for Ante Meridiem ("before noon" in Latin) and PM for Post Meridiem ("after noon"). Since 12:00 noon is noon itself—neither before nor after—the expressions "12 AM" and "12 PM" are inherently contradictory.