密事 is read as みつじ (mitsuji) and means a secret.
みつじ
mitsuji
みそかごと
amorous affair
ぐんじきみつ
military secret
ぐんじひみつ
きみつじこう
confidential matters
みつにゅうこく
smuggling oneself into a country
みつど
density
みつゆ
smuggling
みっせつ
being in close proximity
みつばい
illicit sale
みっしゅう
crowding together
みっしつ
locked room
みつやく
secret agreement