Iceberg (noun)

1. A large piece of ice that has broken off a glacier or ice shelf and is floating in the sea.
2. A large, hidden, or underlying problem or difficulty that is only a small part of it visible.

Origin:

Early 17th century: from dutch ijsberg, from ijs "ice" + berg "mountain".

Examples:

1. The ship hit an iceberg and sank.
2. The iceberg was the size of a small island.
3. The icebergs in the Arctic are melting at an alarming rate.
4. The company's financial troubles were just the tip of the iceberg.
5. The iceberg was a spectacular sight as it floated in the bay.