The word "graviest" is spelled with a "v" because the ending "est" indicates the superlative degree of an adjective or adverb. In this case, "gravy" is the noun being modified, and "graviest" means the most gravy-like or rich in gravy. The pronunciation of "graviest" is [ˈɡreɪviɪst], with stress placed on the first syllable and the "a" pronounced with a long "a" sound. The "i" is pronounced as an "ee" sound, and the final "est" is pronounced with a short "e" sound.