Zyzyvva: the last word in the English dictionary (if you can find one that lists it).

Zyzyvva is a calligraphic term describing a method of letter drawing that is almost impossible to describe in words. It involves the way the hand, pen and nib is held to create a certain type of swish for a particular stroke. The stroke created goes from being very thin to thick in a single quick movement.

Doing it correctly and smoothly is very difficult: when I worked for a calligraphy house, I could never get it exactly correct.