chironomy (in the classical sense, and it's not used much otherwise) was the use of hand gestures without an accompanying score

It was a branch of rhetoric. I have a reprint of a manual of chironomy from the early in the 19th century and it's a listing of gestures to be used for rhetorical effect when declaiing a speech or when acting on the stage. I ran across the book while researching traditional gestures in 18th and 19th century performances of Hamlet (as a lark, not for monetary gain).

I have never run across the word to mean what a choir director does, but I have seen some of those people use hand gestures to urge the singers along.

Ceci n'est pas un seing.