Cayenne is a finely ground brownish-red spice powder that comes from grinding dried peppers.
Cinnamon is a finely ground reddish spice powder that comes from the inner bark of the cinnamon tree.
Cayenne provides heat, a burn to the tongue, not the type of burn that injures, but one that makes sure that the tastebuds are aware there was capsaicin present in the food.
Cinnamon provides flavor to both savory and sweet dishes, and a scent reminiscent of winter holidays and childhood memories.
They are different, but oh so dangerously similar. For example, they are both sold in the spice aisle of the grocery store, both packaged in the same sized jars. They are often next to each other in alphabetical order on home spice racks, though chives and cilantro may interfere in their neighborly arrangement.
There are similarities in color, and in texture. But they are more different than alike. The principal difference, the so very critical difference becomes apparent when used in recipes that call for one or the other. For example, if a person has a craving for chocolate chip cookies and the recipe calls for 1/8 teaspoon of cinnamon, then there can be no substitutions: cinammon will provide a delicious and possibly addictive sweet treat, suitable for sharing with family and friends or consuming by one’s self in a single delicious snack; cayenne pepper will corrupt the recipe, destroy the dough, give you an unpalatable cookie that one’s child will spit out and one’s husband will sample with an amused grin before asking if perhaps glasses should be worn in the kitchen to differentiate spice bottles.