契機
けいき · keiki · JLPT N3 · noun
opportunity
🔑 契 notch/pact + 機 trigger, key moment (as in 機会) = the moment that sets it off
契 first meant notches cut in a tally to seal an agreement. 機 was the trigger of a crossbow, so it came to mean the decisive moment. A 契機 is the turning point or occasion that sets something in motion. Sound hook: keiki ≈ cake key.