Hidden means placed out of sight or kept secret, either on purpose or by chance. When you hide something, you put it where others can't see it. A hidden treasure might be buried underground or tucked behind a loose brick in an old wall. A hidden door in a library bookcase leads to a secret room. Your sister's hidden diary stays concealed under her mattress.

Things can also be hidden without anyone deliberately hiding them. A scientific truth might stay hidden for centuries until someone makes the right discovery. A hidden talent for drawing might surprise everyone, including yourself, when you finally try sketching. When someone has a hidden agenda, they have secret motives they aren't sharing openly.

The word suggests something that exists but isn't immediately obvious. Hidden can describe physical objects (a hidden key), feelings (hidden fear), or meanings (the hidden message in a story). When you finally discover something that was hidden, you often feel that satisfying moment of revelation, like when you spot your friend during hide-and-seek or suddenly understand a riddle's hidden meaning.