Answer: The best definition for the prefix "inter-" is 2. between.
Step-by-step explanation: The word "inter-" is a prefix, which means it is added before a root word. Moreover, "inter-" is used to form adjectives and nouns and its meaning is "between" or "mutually/reciprocally". Many English words are prefixed with "inter-" such as the nouns "interaction" and "intercommunication" and the adjectives "interactive" and "intercultural".