Tickler

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

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.