Answer: clamsup

AnswerCrossword Clue
CLAMSUP

Forgoes conversation

CLAMSUP

Decides to stop talking

CLAMSUP

Refuses to talk

CLAMSUP
Refuses to talk: Slang.
CLAMSUP
Stops talking: Slang.
CLAMSUPRefuses to spill the beans
CLAMSUPButtons one's lip
CLAMSUPIs tight-lipped
CLAMSUPStops talking suddenly
CLAMSUPStops yapping
CLAMSUPZips one's lip