And their locations have remained secret for four hundred years.

I've tried to keep it secret for the moment, to stop any panic.

And too secret for anyone to know quite who was responsible.

"I kept it secret for a long time," she said.

Much of this military work would remain secret for many years.

Whatever it is, it's too secret for an open telephone line.

The proceedings are secret for a period of fifty years.

I did not see how he could keep it secret for much longer, but that was his business.

"Suppose we try to keep it secret for a while."

The research has been secret, for reasons you will come to understand.