Those sealed in secrecy? (4)
I believe the answer is:
lips
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for lips that I've seen before include "Top edges of vessels" , "Take, O take those - away (Measure for Measure)" , "Brims, rims" , "Rim of the mouth" , "Fleshy folds on the face" .)