Tickler

·noun One who, or that which, tickles.

II. Tickler ·noun Something puzzling or difficult.

III. Tickler ·noun A prong used by coopers to extract bungs from casks.

IV. Tickler ·noun A book containing a memorandum of notes and debts arranged in the order of their maturity.

tickler
A common name among merchants and bankers for a book in which a register of notes or debts is kept, ...

Dictionary of American Words And Phrases by John Russell Bartlett.