Thought it was an old-fashioned spelling then learned it was its own word

I was reading about the French Revolution and this quote appeared: “The tocsin we are about to sound is not a warning signal; it sounds the charge on the enemies of our country..."

I thought, hm, did he mean toxin? Doesn't sound like it. Looked up tocsin and it means "an alarm bell or signal." Seems to be used more in a metaphorical sense, as in, "He used his resignation as a tocsin to warn of the danger of dictatorship."