緘口〔缄-〕 gaam¹ hau² {jiān kǒu}

keep secret; to keep one's mouth shut; to hold one's tongue; to say nothing

緘口不言〔缄---〕 gaam¹ hau² bat¹ jin⁴ {jiān kǒu bù yán}

1. lips sealed and not saying anything (idiom); fig. to omit mention (of a non-person or embarrassing topic)
2. to censor