tickler

/ˈtɪklər/
noun
  1. A person or thing that tickles.
    • The feather duster made a good tickler for the baby's feet.
    • He was known as the class tickler, always making his friends laugh.
    • The cat's whiskers were a gentle tickler on her cheek.
  2. A file or system used as a reminder for tasks or appointments; a tickler file.
    • She kept a tickler on her desk with notes for upcoming deadlines.
    • The assistant organized a tickler system to ensure nothing was forgotten.
    • He checked his tickler every morning to see what meetings he had.
  3. A difficult or puzzling question or problem.
    • The detective faced a tickler that took days to solve.
    • The riddle was a tickler that stumped everyone at the party.
    • The math problem was a real tickler for the students.