Adding the suffix -able to a root word forms which part of speech?

I'd say that it would be an adverb. Adding -itis makes a noun, so it wouldn't be a noun. Adverb is pretty much a verb but with a little more special flavors on it. :)

brutus overlooks that the majority of the crowd served julius caesar the military general. he appeals to their citizenship as romans by calling them first by that name in his salutation: "romans, countrymen, lovers." mark antony, however, speaks in terms understood by the military, by calling them first by, "friends, romans, countrymen." he recalls not only caesar the general but caesar the friend, whose body they see covered with stab wounds.