KanjiJLPT N2
Secrecy

secrecy, density (pop), minuteness, carefulness

Mnemonic

Under a roof carved deep inside a mountain, Secrecy is invariably absolute. The mountain's rock is so dense that no signal escapes, and the roof seals everything from view — a perfect hidden vault no outsider will ever find.
Additional thoughts
Visualize a bunker sealed beneath a mountain with a stone roof. The density of the mountain itself mirrors the kanji's extended meaning of tightly packed, impenetrable closeness. Invariably — no exceptions, ever.
Quick recall
A roof buried in a mountain invariably ensures total secrecy.

Details

The keyword for 密 is secrecy. This kanji conveys the idea of something being hidden, concealed, or kept closely guarded from others. It encompasses notions of confidentiality, privacy, and things done covertly or in a clandestine manner. It also extends to meanings of density and closeness, as in things packed tightly together, suggesting an impenetrable quality that keeps what is inside from being seen or known.
On'yomi
みつ
Kun'yomi
ひそ.か