
Cinnamon syrup is a sugar syrup infused with cinnamon bark, used to sweeten and spice a drink at the same time.
Sweetness and spice arrive together, and the spice is easy to add to a plain syrup — at the cost of clouding the drink, since ground cinnamon never dissolves. Which bark it was made from matters more than most recipes admit.
Cassia versus Ceylon syrup
Cassia is the loud, hot, familiar cinnamon and Ceylon is delicate and sweet, and most sticks sold are cassia, so a syrup made from Ceylon needs more bark for the same strength.
Cinnamon schnapps and liqueurs
Alcoholic, often extremely sweet, and usually flavored rather than infused; they bring the spice and rewrite the strength of the drink.
Refrigerated in a sealed bottle for a couple of weeks. Cinnamon syrup tends to outlast a plain one, since cinnamaldehyde is mildly antimicrobial, but this is a syrup and not a preservative: judge it by smell and by whether it has clouded.