'Secret' in the Bible

At the carved images near Gilgal he returned and said, “King Eglon, I have a secret message for you.” The king called for silence, and all his attendants left him.

While the men in ambush were waiting in her room, she called out to him, “Samson, the Philistines are here!” But he snapped the bowstrings as a strand of yarn snaps when it touches fire. The secret of his strength remained unknown.