過去
かこ · kako · JLPT N3 · noun
past
⏳ 過去 = pass by + gone away: what has passed and gone is the past
過 (ka) means to pass or go by, as in 過ぎる. 去 (ko) means to leave or depart, as in 去年, last year. Time that has gone by and left is the past. Kako, the past.
去 — 土 earth on top + 厶 (originally 凵, a vessel/container) below
Originally a pictograph showing a person (大) departing from an enclosed area or vessel, suggesting leaving or going away. Over time the top simplified to 土 and the bottom to 厶. The core meaning 'to go, to leave, to depart' has remained stable since ancient Chinese.