sticker sticker /ˈstɪkɝ/

noun

1. A short knife with a pointed blade used for piercing or stabbing  ( sticker , dagger )
   a short knife with a pointed blade used for piercing or stabbing
    The assassin hid a sharp dagger in his boot.
   The assassin hid a sharp dagger in his boot.
   
   
2. A particularly difficult or baffling question or problem  ( poser , sticker , stumper , toughie [Informal] )
   a particularly difficult or baffling question or problem
   
3. An adhesive label  ( gummed label , paster , sticker )
   an adhesive label
   
   
4. A small sharp-pointed tip resembling a spike on a stem or leaf  ( pricker , prickle , spikelet , spine , sticker , thorn )
   a small sharp-pointed tip resembling a spike on a stem or leaf