From the ArcaMax Publishing, Vocabulary Newsletter:
http://www.arcamax.com/news/vocabulary/s-565210-527403
potentate \POH-tuhn-tayt\ (noun) - One who possesses great power or
sway; a ruler, sovereign, or monarch.
"When the Vizerine has been much younger, she had been taken a slave
for three weeks and forced to perform services arduous and demeaning
for a provincial potentate -- who bore such a resemblance to her
present cook at Court that it all but kept her out of the kitchen." --
Samuel R. Delany, 'Tales of Neveryon'
Potentate derives from Late Latin potentatus, "a powerful person,"
from Latin potentatus, "power, especially political power; supremacy,"
from potens, "able, powerful," from posse, "to be able." It is related
to potent, "powerful," and potential, "having possibility or
capability."