godan verb (-mu), transitive verb
shut one's mouth; hold one's tongue; keep silent
Almost always used in the phrase 口をつぐむ (to shut one's mouth, to keep silent). The verb alone is rarely used.
See also: 口をつぐむ
彼は何も言わずに口をつぐんだ。
He shut his mouth without saying anything.
When that topic comes up, everyone clams up.