Which of the following does not end with ff?

The correct answer is: Employee

The most frequent double-letter combinations ae ee, ll, ss, oo, tt, ff, rr, nn, pp, and cc. The double letters that occur most commonly at the end of words are ee, ll, ss, and ff. There is two words 'employee', and 'tariff'. Both words end with double letter (ee and ff). So, the word 'employee' does not end with 'ff'.