古 gǔ old

old; ancient

How it came to be

指事 · Indicative

A sign that points at an idea, often a mark added to a simple drawing.

The oldest form sets a mouth under a second shape, which some read as a shield and others as a piece of food.

Adjective/bound root for "ancient, from long ago": historically old, not "old" as in aged or worn.
Different from 老 lǎo, which means old in the sense of a person's age or something worn out by time; 古 specifically points back to antiquity/history.
古代 gǔdài "ancient times" and 古老 gǔlǎo "ancient, age-old" (of civilizations, traditions) are the core words; 考古 kǎogǔ "archaeology" is the field name.
古怪 gǔguài "strange, eccentric" is a separate, unrelated-feeling extension meaning "odd", not "ancient".