I am sure I’ve never seen this word before I found it in “The Case of the Lame Snail”, in The Complete Casebook of Herlock Sholmes. I had to stop reading and look it up. From the context, I thought it might mean something like the center of attention. I wasn’t entirely wrong.
Cynosure – someone or something that strongly attracts attention or admiration; something serving for guidance or direction
Usage: “Herlock Sholmes was the cynosure of all eyes as he picked up the football and drew from his pocket a large magnifying glass.”
In this case, Sholmes’ help is required to determine the winner of a football (soccer) match. Dr Jotson is concerned at the end of the story that Sholmes made a mistake, the only one he had ever known Sholmes to make. You will have to read “The Case of the Lame Snail” yourself to determine if Sholmes did in fact make a mistake.