He's accused of having a 'hidden agenda'. [=a secret plan]
His suggestions have a 'hidden' [='secret'] purpose.
There was a 'hidden' flaw in the airplane's design.
(..) ...the Ring and the Dark Lord. Frodo... ...he must never find it. All right. We put it away. We keep it hidden. We never speak of it again. No one knows it's here,do they? Do they,Gandalf? There is one other who knew that Bilbo had the Ring. I looked everywhere for the creature Gollum. (..)2001 The Lord of the Rings: The Fellowship of the Ring