Longman Dictionary of Contemporary English
close-mouthed
adjective
EXAMPLES FROM CORPUS
▪ Emma suspected some of the other children had harassed her, but even to Emma, Ruth had been close-mouthed.
Usage examples of "close-mouthed".
They were a close-mouthed lot about what went on inside their chapter house.
He was a Down Easter in French disguise -- cantankerous, suspicious, close-mouthed, using his accent as a shield more than as a help in communication.