This idiom meaning:
to remain silent regarding a particular subject or circumstance in order to not incriminate yourself
Synonyms:
answer, bridle, button, check, clam, close-lipped, curb, defer, discrete, discretion, evidence, grounds, hold, hush-hush, incriminate, inhibit, keep, law, oath, refrain, refuse, restrain, reticent, silent, suppress, testify, tight-lipped, uncommunicative, unforthcoming, zip