秘密 (mì mì)

secret; private; confidential; clandestine; a secret (CL:個|个[ge4])

Character breakdown

秘 (mì) · 10 strokes

Phonosemantic compound. 礻 represents the meaning and 必 represents the sound. Originally written as 祕. The 礻 component was later corrupted to 禾.
密 (Mì) · 11 strokes

Phonosemantic compound. 山 represents the meaning and 宓 represents the sound.