In colonial times men wore their hair long and tied back in a
ponytail. George Washington and Thomas Jefferson come to mind. What
was the name for this "ponytail" during that time
period?

Dear marv1953,

The tail worn by men in the 18th century was generally simply known as
"queue". However, there were many variants, depending on whether the
person wore natural hair or a wig (as George Washington did), on his
profession and social rank, and of course on his individual
preferences. For example, a very long queue down to the waist, tightly
wrapped with black ribbon, was known as a "Hessian Tail". A similar,
but much shorter tail was called a "pigtail queue". British soldiers
from the lower ranks wore plaited tails that were bound up and hidden
under their hats, so on first sight they appeared to wear short hair.
No particular name except for queue was given to hair that was simply
brushed back and tied up without wrapping it or stuffing it in a hair
bag made from silk or other fabric.

For more information, you may want to have a look at the respective
sections of these websites on fashion in Colonial times:

Colonial Clothing: The Revolution and the New Republic, 1775-1800
http://www.englishcountrydancing.org/colonial7.html

Colonial Clothing: Growth and Change in the Colonies, 1675-1775 -
Costume of the Men
http://www.englishcountrydancing.org/colonial5.html#anchor506052

Regards,
Scriptor