'Secret' in the Bible

Having made clear to us the secret of his purpose, in agreement with the design which he had in mind, to put into his hands

How by revelation the secret was made clear to me, as I said before in a short letter,

By the reading of which you will be clear about my knowledge of the secret of Christ;

And make all men see what is the ordering of the secret which from the first has been kept in God who made all things;

For the things which are done by them in secret it is shame even to put into words.

This is a great secret: but my words are about Christ and the church.

And for me, that words may be given to me in the opening of my mouth, to make clear without fear the secret of the good news,