Tickler /(?)/

Tic·kler

Tickler

n.
  1. One who, or that which, tickles.
  2. Something puzzling or difficult.
  3. A book containing a memorandum of notes and debts arranged in the order of their maturity. [Com. Cant, U. S.]
  4. A prong used by coopers to extract bungs from casks. [Eng.]