The crossword solution for the term MATTER OR 'HERO' PREFIX is ANTI, which is a four-letter word. The prefix 'ANTI' is derived from the Greek word 'ANTI, ' meaning 'AGAINST, ' and is used to form words that express opposition or resistance. It is commonly used in words such as 'antibody, ' 'ANTIPATHY, ' and 'ANTISEPTIC.' In the context of the term MATTER OR 'HERO' PREFIX, the prefix 'ANTI' could be used to describe a person who opposes a hero or a matter that is contrary to a hero's actions.