Final answer:
The prefix meaning "against" includes both 'Contra-' and 'Anti-'. These prefixes are used in English to denote opposition, as seen in words like 'contradict' and 'antivirus'.
Step-by-step explanation:
The prefix meaning "against" is both Contra- and Anti-. These prefixes are used in a variety of English words to indicate opposition or contrast. For instance, contradict means to speak against or to assert the opposite, illustrating the use of 'contra-', while antivirus refers to software designed to detect and destroy computer viruses, showing the usage of 'anti-'.