A term of respect appended to the recipient's name on a letter.

key

(computing) key / (music) key

key (tool for opening or locking something) / key; clue (important fact for solving something) / lock

落ちる: to fall

(chiefly women's speech) first person singular pronoun: I, me

to fall / (computing) to go down (as when a computer or application becomes unresponsive) / (electrical engineering, of a circuit breaker) to trip / (informal) to fail an examination

private; mine

(polite) first-person singular pronoun: I, me

a personal or private matter / (by extension) selfishness