The word that has a prefix meaning "against" is "contradict."
The word "contradict" has a prefix that means "against." The prefix "contra-" means "against" or "opposite." To determine which word has a prefix that means "against," you can break down the words and analyze their prefixes. In this case, "excoriate" does not contain the prefix "contra-," "distend" does not contain the prefix "contra-," and "abnormal" does not contain the prefix "contra-." Therefore, the word "contradict" is the correct answer.
