守口如瓶

lit. to guard one's mouth like a closed bottle (idiom); tight-lipped / reticent / not breathing a word

as / as if / such as

mouth / classifier for things with mouths (people, domestic animals, cannons, wells etc) / classifier for bites or mouthfuls

bottle / vase / pitcher / CL:個|个[ge4] / classifier for wine and liquids

variant of 瓶[ping2]

to guard / to defend / to keep watch / to abide by the law / to observe (rules or ritual) / nearby / adjoining