tocsin

n. warning signal, alarm; alarm bell, ringing of a warning bell

A tocsin consists of a signal of alarm given by the ringing of a  bell, and hence any warning or danger signal. The earliest form of the word in  English appears as toclesaine, borrowed from the Old French touque-sain (from toquer (to strike), compare toucher), combined with sin (modern French signe (a signal) from the Latin signum). The use of touch and its cognate forms with the idea of giving a sound also appears in the word tucket, Italian toccata, which probably originally meant a signal given by tap of drum, but subsequently always applied to a flourish or fanfare on a trumpet.
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Noun
1. the sound of an alarm (usually a bell)
(synonym) alarm bell
(hypernym) alarm, alert, warning signal, alarum
2. a bell used to sound an alarm
(synonym) warning bell
(hypernym) bell

n. tocsin, warning signal, alarm

(n.)
An alarm bell, or the ringing of a bell for the purpose of alarm.