sticker

/ˈstɪkər/
noun
  1. A small piece of paper, plastic, or other material with a sticky back, used for decoration, labeling, or identification.
    • She put a smiley face sticker on her notebook.
    • He collected stickers of his favorite cartoon characters.
    • The fruit had a small sticker showing the price.
  2. A sharp point or thorn on a plant.
    • I got a sticker stuck in my finger from the rose bush.
    • The burrs have tiny stickers that cling to clothing.
    • Be careful of the stickers on that cactus.
  3. A persistent or difficult person or thing (informal).
    • He's a sticker when it comes to following rules.
    • That math problem was a real sticker.
    • The final exam was a sticker for most students.