キー

1. 1key (for a lock) Translated by Jiyomi
2. 2key (of a piano, organ, computer keyboard, etc.) Translated by Jiyomi
3. 3key Translated by Jiyomi
4. 4key (to solving something) ; clue Translated by Jiyomi
5. 5key (person, point, etc.) ; most important Translated by Jiyomi

JMdict entry 1040680 · frequency rank 50. Source and licence.