Barnacle (noun)

1. A marine crustacean that attaches itself to rocks, ships, and other underwater surfaces.
2. Something that clings tenaciously to something else and is difficult to remove.

Origin:

Middle english: from old french barnacle, perhaps of celtic origin.

Examples:

1. The rocks at the shore were covered in barnacles.
2. The bottom of the ship was covered in barnacles, slowing its speed.
3. Barnacles can survive in salt water for extended periods of time.
4. He compared his ex-girlfriend to a barnacle, saying she would not let go of him.
5. The barnacle is a type of crustacean that belongs to the Cirripedia class.