The spelling of "most eristical" is a tricky one. The word "eristical" is pronounced /əˈrɪstɪk(ə)l/ and means "given to disputation or argumentation; contentious." When adding "most" to the beginning of the word, it can be tempting to spell it as "most eristic," but the correct spelling includes the full adjective form of "eristical." Therefore, it is spelled "most eristical" /məʊst əˈrɪstɪk(ə)l/. It is important to pay attention to the full form of the adjective when using superlative forms in English.